diff --git a/explorer/BUILD b/explorer/BUILD
index 441e368af3516..0fbfe3af62fa4 100644
--- a/explorer/BUILD
+++ b/explorer/BUILD
@@ -24,7 +24,7 @@ cc_library(
     deps = [
         "//common:error",
         "//common:ostream",
-        "//explorer/common:trace_stream",
+        "//explorer/base:trace_stream",
         "//explorer/parse_and_execute",
         "@llvm-project//llvm:Support",
     ],
diff --git a/explorer/README.md b/explorer/README.md
index ba8862b868742..9b9e8f34c950a 100644
--- a/explorer/README.md
+++ b/explorer/README.md
@@ -41,19 +41,19 @@ RTTI switches, so that the compiler can help ensure the code is updated when a
 new type is added.
 
 `explorer` never uses plain pointer types directly. Instead, we use the
-[`Nonnull<T*>`](common/nonnull.h) alias for pointers that are not nullable, or
+[`Nonnull<T*>`](base/nonnull.h) alias for pointers that are not nullable, or
 `std::optional<Nonnull<T*>>` for pointers that are nullable.
 
 Many of the most commonly-used objects in `explorer` have lifetimes that are
 tied to the lifespan of the entire Carbon program. We manage the lifetimes of
-those objects by allocating them through an [`Arena`](common/arena.h) object,
+those objects by allocating them through an [`Arena`](base/arena.h) object,
 which can allocate objects of arbitrary types, and retains ownership of them. As
 of this writing, all of `explorer` uses a single `Arena` object, we may
 introduce multiple `Arena`s for different lifetime groups in the future.
 
 For simplicity, `explorer` generally treats all errors as fatal. Errors caused
 by bugs in the user-provided Carbon code should be reported with the error
-builders in [`error_builders.h`](common/error_builders.h). Errors caused by bugs
+builders in [`error_builders.h`](base/error_builders.h). Errors caused by bugs
 in `explorer` itself should be reported with
 [`CHECK` or `FATAL`](../common/check.h).
 
diff --git a/explorer/ast/BUILD b/explorer/ast/BUILD
index 0ec9b6b860723..f192094f7c79e 100644
--- a/explorer/ast/BUILD
+++ b/explorer/ast/BUILD
@@ -51,11 +51,11 @@ cc_library(
         "//common:error",
         "//common:indirect_value",
         "//common:ostream",
-        "//explorer/common:arena",
-        "//explorer/common:decompose",
-        "//explorer/common:error_builders",
-        "//explorer/common:nonnull",
-        "//explorer/common:source_location",
+        "//explorer/base:arena",
+        "//explorer/base:decompose",
+        "//explorer/base:error_builders",
+        "//explorer/base:nonnull",
+        "//explorer/base:source_location",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -81,7 +81,7 @@ cc_test(
     deps = [
         ":ast",
         ":ast_test_matchers",
-        "//explorer/common:arena",
+        "//explorer/base:arena",
         "//testing/util:gtest_main",
         "@com_google_googletest//:gtest",
     ],
@@ -93,7 +93,7 @@ cc_test(
     deps = [
         ":ast",
         ":paren_contents",
-        "//explorer/common:arena",
+        "//explorer/base:arena",
         "//testing/util:gtest_main",
         "@com_google_googletest//:gtest",
         "@llvm-project//llvm:Support",
@@ -109,8 +109,8 @@ cc_library(
     name = "paren_contents",
     hdrs = ["paren_contents.h"],
     deps = [
-        "//explorer/common:error_builders",
-        "//explorer/common:source_location",
+        "//explorer/base:error_builders",
+        "//explorer/base:source_location",
     ],
 )
 
@@ -120,7 +120,7 @@ cc_test(
     deps = [
         ":ast",
         ":paren_contents",
-        "//explorer/common:arena",
+        "//explorer/base:arena",
         "//testing/util:gtest_main",
         "@com_google_googletest//:gtest",
         "@llvm-project//llvm:Support",
@@ -133,7 +133,7 @@ cc_test(
     deps = [
         ":ast",
         ":paren_contents",
-        "//explorer/common:arena",
+        "//explorer/base:arena",
         "//testing/util:gtest_main",
         "@com_google_googletest//:gtest",
         "@llvm-project//llvm:Support",
@@ -149,10 +149,10 @@ cc_library(
         "//common:check",
         "//common:error",
         "//common:ostream",
-        "//explorer/common:error_builders",
-        "//explorer/common:nonnull",
-        "//explorer/common:source_location",
-        "//explorer/common:trace_stream",
+        "//explorer/base:error_builders",
+        "//explorer/base:nonnull",
+        "//explorer/base:source_location",
+        "//explorer/base:trace_stream",
         "@llvm-project//llvm:Support",
     ],
 )
diff --git a/explorer/ast/ast.h b/explorer/ast/ast.h
index 1b30d10edaba3..28061e39d3100 100644
--- a/explorer/ast/ast.h
+++ b/explorer/ast/ast.h
@@ -9,7 +9,7 @@
 
 #include "explorer/ast/declaration.h"
 #include "explorer/ast/library_name.h"
-#include "explorer/common/nonnull.h"
+#include "explorer/base/nonnull.h"
 
 namespace Carbon {
 
diff --git a/explorer/ast/ast_node.h b/explorer/ast/ast_node.h
index 005df3d4fa48d..525c3e7f418b8 100644
--- a/explorer/ast/ast_node.h
+++ b/explorer/ast/ast_node.h
@@ -6,7 +6,7 @@
 #define CARBON_EXPLORER_AST_AST_NODE_H_
 
 #include "explorer/ast/ast_rtti.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/source_location.h"
 #include "llvm/Support/Casting.h"
 
 namespace Carbon {
diff --git a/explorer/ast/ast_test_matchers_test.cpp b/explorer/ast/ast_test_matchers_test.cpp
index 64a1c8bf47425..731577294d92f 100644
--- a/explorer/ast/ast_test_matchers_test.cpp
+++ b/explorer/ast/ast_test_matchers_test.cpp
@@ -11,7 +11,7 @@
 #include "explorer/ast/expression.h"
 #include "explorer/ast/pattern.h"
 #include "explorer/ast/statement.h"
-#include "explorer/common/arena.h"
+#include "explorer/base/arena.h"
 
 namespace Carbon::Testing {
 namespace {
diff --git a/explorer/ast/bindings.h b/explorer/ast/bindings.h
index afc210f561a71..e5b8ac963fc29 100644
--- a/explorer/ast/bindings.h
+++ b/explorer/ast/bindings.h
@@ -10,7 +10,7 @@
 
 #include "common/ostream.h"
 #include "explorer/ast/clone_context.h"
-#include "explorer/common/nonnull.h"
+#include "explorer/base/nonnull.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringExtras.h"
 
diff --git a/explorer/ast/clone_context.h b/explorer/ast/clone_context.h
index a77158ce9ea5e..7be00a42d538d 100644
--- a/explorer/ast/clone_context.h
+++ b/explorer/ast/clone_context.h
@@ -11,7 +11,7 @@
 
 #include "common/check.h"
 #include "explorer/ast/ast_rtti.h"
-#include "explorer/common/arena.h"
+#include "explorer/base/arena.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/Support/Casting.h"
 
diff --git a/explorer/ast/declaration.h b/explorer/ast/declaration.h
index b3f11f506f502..26d6d32866e1a 100644
--- a/explorer/ast/declaration.h
+++ b/explorer/ast/declaration.h
@@ -20,8 +20,8 @@
 #include "explorer/ast/return_term.h"
 #include "explorer/ast/statement.h"
 #include "explorer/ast/value_node.h"
-#include "explorer/common/nonnull.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/nonnull.h"
+#include "explorer/base/source_location.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/Support/Compiler.h"
 
diff --git a/explorer/ast/element.h b/explorer/ast/element.h
index 859582fa6d945..07b7d56db9492 100644
--- a/explorer/ast/element.h
+++ b/explorer/ast/element.h
@@ -11,8 +11,8 @@
 
 #include "common/ostream.h"
 #include "explorer/ast/ast_rtti.h"
-#include "explorer/common/decompose.h"
-#include "explorer/common/nonnull.h"
+#include "explorer/base/decompose.h"
+#include "explorer/base/nonnull.h"
 #include "llvm/ADT/PointerUnion.h"
 
 namespace Carbon {
diff --git a/explorer/ast/element_test.cpp b/explorer/ast/element_test.cpp
index da1c8663a1046..b759c498e1402 100644
--- a/explorer/ast/element_test.cpp
+++ b/explorer/ast/element_test.cpp
@@ -13,7 +13,7 @@
 #include "explorer/ast/declaration.h"
 #include "explorer/ast/expression.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/arena.h"
+#include "explorer/base/arena.h"
 #include "llvm/Support/Casting.h"
 
 namespace Carbon::Testing {
diff --git a/explorer/ast/expression.cpp b/explorer/ast/expression.cpp
index e1263373770ff..0342bb483a675 100644
--- a/explorer/ast/expression.cpp
+++ b/explorer/ast/expression.cpp
@@ -9,8 +9,8 @@
 
 #include "explorer/ast/pattern.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/error_builders.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/error_builders.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/raw_ostream.h"
diff --git a/explorer/ast/expression.h b/explorer/ast/expression.h
index 34b6c52d85074..cb9206f11b792 100644
--- a/explorer/ast/expression.h
+++ b/explorer/ast/expression.h
@@ -19,8 +19,8 @@
 #include "explorer/ast/expression_category.h"
 #include "explorer/ast/paren_contents.h"
 #include "explorer/ast/value_node.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/source_location.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/Support/Compiler.h"
 
diff --git a/explorer/ast/expression_test.cpp b/explorer/ast/expression_test.cpp
index d3e39786ff4ed..4acd0e55729b4 100644
--- a/explorer/ast/expression_test.cpp
+++ b/explorer/ast/expression_test.cpp
@@ -10,7 +10,7 @@
 #include <string>
 
 #include "explorer/ast/paren_contents.h"
-#include "explorer/common/arena.h"
+#include "explorer/base/arena.h"
 #include "llvm/Support/Casting.h"
 
 namespace Carbon::Testing {
diff --git a/explorer/ast/paren_contents.h b/explorer/ast/paren_contents.h
index 526802fc49cfe..95382dc8d819f 100644
--- a/explorer/ast/paren_contents.h
+++ b/explorer/ast/paren_contents.h
@@ -9,8 +9,8 @@
 #include <string>
 #include <vector>
 
-#include "explorer/common/error_builders.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/error_builders.h"
+#include "explorer/base/source_location.h"
 
 namespace Carbon {
 
diff --git a/explorer/ast/pattern.cpp b/explorer/ast/pattern.cpp
index 8b36d3ee5af20..0699fd9baffe1 100644
--- a/explorer/ast/pattern.cpp
+++ b/explorer/ast/pattern.cpp
@@ -10,8 +10,8 @@
 #include "explorer/ast/expression.h"
 #include "explorer/ast/impl_binding.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/error_builders.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/error_builders.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/Casting.h"
 
diff --git a/explorer/ast/pattern.h b/explorer/ast/pattern.h
index fe2934b1b79af..e7d5d1bd2c13d 100644
--- a/explorer/ast/pattern.h
+++ b/explorer/ast/pattern.h
@@ -17,7 +17,7 @@
 #include "explorer/ast/expression.h"
 #include "explorer/ast/expression_category.h"
 #include "explorer/ast/value_node.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/source_location.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/STLFunctionalExtras.h"
 
diff --git a/explorer/ast/pattern_test.cpp b/explorer/ast/pattern_test.cpp
index f3c1c00005eb8..36de0d5aa30d6 100644
--- a/explorer/ast/pattern_test.cpp
+++ b/explorer/ast/pattern_test.cpp
@@ -9,7 +9,7 @@
 
 #include "explorer/ast/expression.h"
 #include "explorer/ast/paren_contents.h"
-#include "explorer/common/arena.h"
+#include "explorer/base/arena.h"
 #include "llvm/Support/Casting.h"
 
 namespace Carbon::Testing {
diff --git a/explorer/ast/return_term.h b/explorer/ast/return_term.h
index b3c7ff2eec649..b7af6b6b3f0b2 100644
--- a/explorer/ast/return_term.h
+++ b/explorer/ast/return_term.h
@@ -12,8 +12,8 @@
 #include "common/ostream.h"
 #include "explorer/ast/clone_context.h"
 #include "explorer/ast/expression.h"
-#include "explorer/common/nonnull.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/nonnull.h"
+#include "explorer/base/source_location.h"
 
 namespace Carbon {
 
diff --git a/explorer/ast/statement.cpp b/explorer/ast/statement.cpp
index cedb508cc5acf..830af0a20ead9 100644
--- a/explorer/ast/statement.cpp
+++ b/explorer/ast/statement.cpp
@@ -6,7 +6,7 @@
 
 #include "common/check.h"
 #include "explorer/ast/declaration.h"
-#include "explorer/common/arena.h"
+#include "explorer/base/arena.h"
 #include "llvm/Support/Casting.h"
 
 namespace Carbon {
diff --git a/explorer/ast/statement.h b/explorer/ast/statement.h
index 716afdd8ccb41..a157797f2ebaa 100644
--- a/explorer/ast/statement.h
+++ b/explorer/ast/statement.h
@@ -16,8 +16,8 @@
 #include "explorer/ast/pattern.h"
 #include "explorer/ast/return_term.h"
 #include "explorer/ast/value_node.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/source_location.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/Support/Compiler.h"
 
diff --git a/explorer/ast/static_scope.cpp b/explorer/ast/static_scope.cpp
index d9f050848dffe..e0cbde161c712 100644
--- a/explorer/ast/static_scope.cpp
+++ b/explorer/ast/static_scope.cpp
@@ -7,7 +7,7 @@
 #include <optional>
 
 #include "common/ostream.h"
-#include "explorer/common/error_builders.h"
+#include "explorer/base/error_builders.h"
 #include "llvm/ADT/ScopeExit.h"
 #include "llvm/Support/Error.h"
 
diff --git a/explorer/ast/static_scope.h b/explorer/ast/static_scope.h
index 746807c388258..52b575026fdb3 100644
--- a/explorer/ast/static_scope.h
+++ b/explorer/ast/static_scope.h
@@ -10,9 +10,9 @@
 
 #include "common/error.h"
 #include "explorer/ast/value_node.h"
-#include "explorer/common/nonnull.h"
-#include "explorer/common/source_location.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/nonnull.h"
+#include "explorer/base/source_location.h"
+#include "explorer/base/trace_stream.h"
 #include "llvm/ADT/StringMap.h"
 
 namespace Carbon {
diff --git a/explorer/ast/value.cpp b/explorer/ast/value.cpp
index 5db3634f317ec..f406a2a6e32d2 100644
--- a/explorer/ast/value.cpp
+++ b/explorer/ast/value.cpp
@@ -14,8 +14,8 @@
 #include "explorer/ast/element.h"
 #include "explorer/ast/element_path.h"
 #include "explorer/ast/value_transform.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/error_builders.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/error_builders.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/Casting.h"
diff --git a/explorer/ast/value.h b/explorer/ast/value.h
index 87569632af45b..894598e13d0ec 100644
--- a/explorer/ast/value.h
+++ b/explorer/ast/value.h
@@ -18,7 +18,7 @@
 #include "explorer/ast/element_path.h"
 #include "explorer/ast/expression_category.h"
 #include "explorer/ast/statement.h"
-#include "explorer/common/nonnull.h"
+#include "explorer/base/nonnull.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/Support/Compiler.h"
 
diff --git a/explorer/ast/value_node.h b/explorer/ast/value_node.h
index c56a178a9ee06..39b61f547e73f 100644
--- a/explorer/ast/value_node.h
+++ b/explorer/ast/value_node.h
@@ -12,7 +12,7 @@
 #include "explorer/ast/ast_node.h"
 #include "explorer/ast/clone_context.h"
 #include "explorer/ast/expression_category.h"
-#include "explorer/common/nonnull.h"
+#include "explorer/base/nonnull.h"
 
 namespace Carbon {
 
diff --git a/explorer/common/BUILD b/explorer/base/BUILD
similarity index 98%
rename from explorer/common/BUILD
rename to explorer/base/BUILD
index 39cf3b95ee90a..0ab0a545723d3 100644
--- a/explorer/common/BUILD
+++ b/explorer/base/BUILD
@@ -86,7 +86,7 @@ cc_library(
         ":source_location",
         "//common:check",
         "//common:ostream",
-        "//explorer/common:nonnull",
+        "//explorer/base:nonnull",
         "@llvm-project//llvm:Support",
     ],
 )
diff --git a/explorer/common/arena.h b/explorer/base/arena.h
similarity index 98%
rename from explorer/common/arena.h
rename to explorer/base/arena.h
index 807f3c09df759..d473c88f901d4 100644
--- a/explorer/common/arena.h
+++ b/explorer/base/arena.h
@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#ifndef CARBON_EXPLORER_COMMON_ARENA_H_
-#define CARBON_EXPLORER_COMMON_ARENA_H_
+#ifndef CARBON_EXPLORER_BASE_ARENA_H_
+#define CARBON_EXPLORER_BASE_ARENA_H_
 
 #include <any>
 #include <map>
@@ -13,7 +13,7 @@
 #include <utility>
 #include <vector>
 
-#include "explorer/common/nonnull.h"
+#include "explorer/base/nonnull.h"
 #include "llvm/ADT/Hashing.h"
 
 namespace Carbon {
@@ -277,4 +277,4 @@ char Arena::TypeId<T>::id = 1;
 
 }  // namespace Carbon
 
-#endif  // CARBON_EXPLORER_COMMON_ARENA_H_
+#endif  // CARBON_EXPLORER_BASE_ARENA_H_
diff --git a/explorer/common/arena_test.cpp b/explorer/base/arena_test.cpp
similarity index 98%
rename from explorer/common/arena_test.cpp
rename to explorer/base/arena_test.cpp
index 7af4a7f503458..54efce59acb97 100644
--- a/explorer/common/arena_test.cpp
+++ b/explorer/base/arena_test.cpp
@@ -2,7 +2,7 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include "explorer/common/arena.h"
+#include "explorer/base/arena.h"
 
 #include <gtest/gtest.h>
 
diff --git a/explorer/common/decompose.h b/explorer/base/decompose.h
similarity index 92%
rename from explorer/common/decompose.h
rename to explorer/base/decompose.h
index f772c03118205..b588229ffb622 100644
--- a/explorer/common/decompose.h
+++ b/explorer/base/decompose.h
@@ -4,8 +4,8 @@
 //
 // Utilities for types that support the `Decompose` API.
 
-#ifndef CARBON_EXPLORER_COMMON_DECOMPOSE_H_
-#define CARBON_EXPLORER_COMMON_DECOMPOSE_H_
+#ifndef CARBON_EXPLORER_BASE_DECOMPOSE_H_
+#define CARBON_EXPLORER_BASE_DECOMPOSE_H_
 
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/Hashing.h"
@@ -51,4 +51,4 @@ class HashFromDecompose {
 
 }  // namespace Carbon
 
-#endif  // CARBON_EXPLORER_COMMON_DECOMPOSE_H_
+#endif  // CARBON_EXPLORER_BASE_DECOMPOSE_H_
diff --git a/explorer/common/decompose_test.cpp b/explorer/base/decompose_test.cpp
similarity index 95%
rename from explorer/common/decompose_test.cpp
rename to explorer/base/decompose_test.cpp
index 66c6d33c9dc0e..be331d648cdd7 100644
--- a/explorer/common/decompose_test.cpp
+++ b/explorer/base/decompose_test.cpp
@@ -2,7 +2,7 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include "explorer/common/decompose.h"
+#include "explorer/base/decompose.h"
 
 #include <gtest/gtest.h>
 
diff --git a/explorer/common/error_builders.h b/explorer/base/error_builders.h
similarity index 77%
rename from explorer/common/error_builders.h
rename to explorer/base/error_builders.h
index 1ccd40bf845d0..4e72f3dc964fd 100644
--- a/explorer/common/error_builders.h
+++ b/explorer/base/error_builders.h
@@ -2,11 +2,11 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#ifndef CARBON_EXPLORER_COMMON_ERROR_BUILDERS_H_
-#define CARBON_EXPLORER_COMMON_ERROR_BUILDERS_H_
+#ifndef CARBON_EXPLORER_BASE_ERROR_BUILDERS_H_
+#define CARBON_EXPLORER_BASE_ERROR_BUILDERS_H_
 
 #include "common/error.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/source_location.h"
 
 namespace Carbon {
 
@@ -23,4 +23,4 @@ inline auto ProgramError(SourceLocation loc) -> ErrorBuilder {
 
 }  // namespace Carbon
 
-#endif  // CARBON_EXPLORER_COMMON_ERROR_BUILDERS_H_
+#endif  // CARBON_EXPLORER_BASE_ERROR_BUILDERS_H_
diff --git a/explorer/common/error_builders_test.cpp b/explorer/base/error_builders_test.cpp
similarity index 87%
rename from explorer/common/error_builders_test.cpp
rename to explorer/base/error_builders_test.cpp
index 2425cdde4f794..6e46d10780749 100644
--- a/explorer/common/error_builders_test.cpp
+++ b/explorer/base/error_builders_test.cpp
@@ -2,11 +2,11 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#include "explorer/common/error_builders.h"
+#include "explorer/base/error_builders.h"
 
 #include <gtest/gtest.h>
 
-#include "explorer/common/source_location.h"
+#include "explorer/base/source_location.h"
 #include "testing/util/test_raw_ostream.h"
 
 namespace Carbon::Testing {
diff --git a/explorer/common/nonnull.h b/explorer/base/nonnull.h
similarity index 82%
rename from explorer/common/nonnull.h
rename to explorer/base/nonnull.h
index c9f63c3a1685a..2bd6a48d752e0 100644
--- a/explorer/common/nonnull.h
+++ b/explorer/base/nonnull.h
@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#ifndef CARBON_EXPLORER_COMMON_NONNULL_H_
-#define CARBON_EXPLORER_COMMON_NONNULL_H_
+#ifndef CARBON_EXPLORER_BASE_NONNULL_H_
+#define CARBON_EXPLORER_BASE_NONNULL_H_
 
 #include <type_traits>
 
@@ -19,4 +19,4 @@ using Nonnull = T _Nonnull;
 
 }  // namespace Carbon
 
-#endif  // CARBON_EXPLORER_COMMON_NONNULL_H_
+#endif  // CARBON_EXPLORER_BASE_NONNULL_H_
diff --git a/explorer/common/set_file_context_raii_test.cpp b/explorer/base/set_file_context_raii_test.cpp
similarity index 96%
rename from explorer/common/set_file_context_raii_test.cpp
rename to explorer/base/set_file_context_raii_test.cpp
index 61a1b8c86c266..647bf67584832 100644
--- a/explorer/common/set_file_context_raii_test.cpp
+++ b/explorer/base/set_file_context_raii_test.cpp
@@ -5,7 +5,7 @@
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
 
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/trace_stream.h"
 
 namespace Carbon::Testing {
 namespace {
diff --git a/explorer/common/set_program_phase_raii_test.cpp b/explorer/base/set_program_phase_raii_test.cpp
similarity index 96%
rename from explorer/common/set_program_phase_raii_test.cpp
rename to explorer/base/set_program_phase_raii_test.cpp
index 44db34f66761e..0aa659b5706be 100644
--- a/explorer/common/set_program_phase_raii_test.cpp
+++ b/explorer/base/set_program_phase_raii_test.cpp
@@ -5,7 +5,7 @@
 #include <gmock/gmock.h>
 #include <gtest/gtest.h>
 
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/trace_stream.h"
 
 namespace Carbon::Testing {
 namespace {
diff --git a/explorer/common/source_location.h b/explorer/base/source_location.h
similarity index 92%
rename from explorer/common/source_location.h
rename to explorer/base/source_location.h
index cc46cc37f736f..0067bedec4b2c 100644
--- a/explorer/common/source_location.h
+++ b/explorer/base/source_location.h
@@ -2,14 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#ifndef CARBON_EXPLORER_COMMON_SOURCE_LOCATION_H_
-#define CARBON_EXPLORER_COMMON_SOURCE_LOCATION_H_
+#ifndef CARBON_EXPLORER_BASE_SOURCE_LOCATION_H_
+#define CARBON_EXPLORER_BASE_SOURCE_LOCATION_H_
 
 #include <string>
 #include <string_view>
 
 #include "common/ostream.h"
-#include "explorer/common/nonnull.h"
+#include "explorer/base/nonnull.h"
 
 namespace Carbon {
 
@@ -72,4 +72,4 @@ class SourceLocation {
 
 }  // namespace Carbon
 
-#endif  // CARBON_EXPLORER_COMMON_SOURCE_LOCATION_H_
+#endif  // CARBON_EXPLORER_BASE_SOURCE_LOCATION_H_
diff --git a/explorer/common/trace_stream.h b/explorer/base/trace_stream.h
similarity index 97%
rename from explorer/common/trace_stream.h
rename to explorer/base/trace_stream.h
index bd8ef73cb0b5a..515ab7b155184 100644
--- a/explorer/common/trace_stream.h
+++ b/explorer/base/trace_stream.h
@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#ifndef CARBON_EXPLORER_COMMON_TRACE_STREAM_H_
-#define CARBON_EXPLORER_COMMON_TRACE_STREAM_H_
+#ifndef CARBON_EXPLORER_BASE_TRACE_STREAM_H_
+#define CARBON_EXPLORER_BASE_TRACE_STREAM_H_
 
 #include <bitset>
 #include <optional>
@@ -13,8 +13,8 @@
 
 #include "common/check.h"
 #include "common/ostream.h"
-#include "explorer/common/nonnull.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/nonnull.h"
+#include "explorer/base/source_location.h"
 #include "llvm/ADT/ArrayRef.h"
 
 namespace Carbon {
@@ -205,4 +205,4 @@ class SetFileContext {
 
 }  // namespace Carbon
 
-#endif  // CARBON_EXPLORER_COMMON_TRACE_STREAM_H_
+#endif  // CARBON_EXPLORER_BASE_TRACE_STREAM_H_
diff --git a/explorer/fuzzing/BUILD b/explorer/fuzzing/BUILD
index 9edaf6beed245..95e7ff2119e79 100644
--- a/explorer/fuzzing/BUILD
+++ b/explorer/fuzzing/BUILD
@@ -25,7 +25,7 @@ cc_binary(
         "//common:bazel_working_dir",
         "//common:error",
         "//explorer/ast",
-        "//explorer/common:arena",
+        "//explorer/base:arena",
         "//explorer/syntax",
         "//testing/fuzzing:carbon_cc_proto",
         "@com_google_protobuf//:protobuf_headers",
diff --git a/explorer/fuzzing/ast_to_proto_main.cpp b/explorer/fuzzing/ast_to_proto_main.cpp
index 590ca9ed44600..7a62fb5139a83 100644
--- a/explorer/fuzzing/ast_to_proto_main.cpp
+++ b/explorer/fuzzing/ast_to_proto_main.cpp
@@ -14,7 +14,7 @@
 #include "common/bazel_working_dir.h"
 #include "common/error.h"
 #include "explorer/ast/ast.h"
-#include "explorer/common/arena.h"
+#include "explorer/base/arena.h"
 #include "explorer/fuzzing/ast_to_proto.h"
 #include "explorer/syntax/parse.h"
 #include "testing/fuzzing/carbon.pb.h"
diff --git a/explorer/interpreter/BUILD b/explorer/interpreter/BUILD
index bd3f6faa8ac5e..58448fde4ebd1 100644
--- a/explorer/interpreter/BUILD
+++ b/explorer/interpreter/BUILD
@@ -20,10 +20,10 @@ cc_library(
         "//common:error",
         "//common:ostream",
         "//explorer/ast",
-        "//explorer/common:arena",
-        "//explorer/common:error_builders",
-        "//explorer/common:nonnull",
-        "//explorer/common:source_location",
+        "//explorer/base:arena",
+        "//explorer/base:error_builders",
+        "//explorer/base:nonnull",
+        "//explorer/base:source_location",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -43,7 +43,7 @@ cc_library(
         "//common:error",
         "//common:ostream",
         "//explorer/ast",
-        "//explorer/common:trace_stream",
+        "//explorer/base:trace_stream",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -51,7 +51,7 @@ cc_library(
 cc_library(
     name = "dictionary",
     hdrs = ["dictionary.h"],
-    deps = ["//explorer/common:arena"],
+    deps = ["//explorer/base:arena"],
 )
 
 cc_library(
@@ -68,8 +68,8 @@ cc_library(
         "//common:error",
         "//common:ostream",
         "//explorer/ast",
-        "//explorer/common:arena",
-        "//explorer/common:trace_stream",
+        "//explorer/base:arena",
+        "//explorer/base:trace_stream",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -85,10 +85,10 @@ cc_library(
         "//common:error",
         "//common:ostream",
         "//explorer/ast",
-        "//explorer/common:error_builders",
-        "//explorer/common:nonnull",
-        "//explorer/common:source_location",
-        "//explorer/common:trace_stream",
+        "//explorer/base:error_builders",
+        "//explorer/base:nonnull",
+        "//explorer/base:source_location",
+        "//explorer/base:trace_stream",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -99,9 +99,9 @@ cc_library(
     deps = [
         "//common:error",
         "//explorer/ast",
-        "//explorer/common:arena",
-        "//explorer/common:nonnull",
-        "//explorer/common:source_location",
+        "//explorer/base:arena",
+        "//explorer/base:nonnull",
+        "//explorer/base:source_location",
     ],
 )
 
@@ -125,10 +125,10 @@ cc_library(
         "//common:ostream",
         "//explorer/ast",
         "//explorer/ast:expression_category",
-        "//explorer/common:arena",
-        "//explorer/common:error_builders",
-        "//explorer/common:source_location",
-        "//explorer/common:trace_stream",
+        "//explorer/base:arena",
+        "//explorer/base:error_builders",
+        "//explorer/base:source_location",
+        "//explorer/base:trace_stream",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -140,9 +140,9 @@ cc_library(
     deps = [
         "//common:check",
         "//explorer/ast",
-        "//explorer/common:error_builders",
-        "//explorer/common:nonnull",
-        "//explorer/common:trace_stream",
+        "//explorer/base:error_builders",
+        "//explorer/base:nonnull",
+        "//explorer/base:trace_stream",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -156,8 +156,8 @@ cc_library(
         "//common:check",
         "//explorer/ast",
         "//explorer/ast:static_scope",
-        "//explorer/common:arena",
-        "//explorer/common:trace_stream",
+        "//explorer/base:arena",
+        "//explorer/base:trace_stream",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -180,7 +180,7 @@ cc_library(
         ":action",
         "//common:error",
         "//explorer/ast",
-        "//explorer/common:nonnull",
+        "//explorer/base:nonnull",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -216,11 +216,11 @@ cc_library(
         "//common:error",
         "//common:ostream",
         "//explorer/ast",
-        "//explorer/common:arena",
-        "//explorer/common:error_builders",
-        "//explorer/common:nonnull",
-        "//explorer/common:source_location",
-        "//explorer/common:trace_stream",
+        "//explorer/base:arena",
+        "//explorer/base:error_builders",
+        "//explorer/base:nonnull",
+        "//explorer/base:source_location",
+        "//explorer/base:trace_stream",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -238,9 +238,9 @@ cc_library(
         "//common:check",
         "//explorer/ast",
         "//explorer/ast:static_scope",
-        "//explorer/common:error_builders",
-        "//explorer/common:nonnull",
-        "//explorer/common:trace_stream",
+        "//explorer/base:error_builders",
+        "//explorer/base:nonnull",
+        "//explorer/base:trace_stream",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -268,7 +268,7 @@ cc_library(
         "//common:ostream",
         "//explorer/ast",
         "//explorer/ast:expression_category",
-        "//explorer/common:nonnull",
+        "//explorer/base:nonnull",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -283,7 +283,7 @@ cc_library(
     ],
     deps = [
         "//explorer/ast",
-        "//explorer/common:nonnull",
+        "//explorer/base:nonnull",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -299,10 +299,10 @@ cc_library(
     deps = [
         ":action",
         "//explorer/ast",
-        "//explorer/common:arena",
-        "//explorer/common:nonnull",
-        "//explorer/common:source_location",
-        "//explorer/common:trace_stream",
+        "//explorer/base:arena",
+        "//explorer/base:nonnull",
+        "//explorer/base:source_location",
+        "//explorer/base:trace_stream",
         "@llvm-project//llvm:Support",
     ],
 )
diff --git a/explorer/interpreter/action.cpp b/explorer/interpreter/action.cpp
index b9a6557782cc5..ec995c4fe7c65 100644
--- a/explorer/interpreter/action.cpp
+++ b/explorer/interpreter/action.cpp
@@ -15,8 +15,8 @@
 #include "explorer/ast/declaration.h"
 #include "explorer/ast/expression.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/source_location.h"
 #include "explorer/interpreter/stack.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/Casting.h"
diff --git a/explorer/interpreter/action.h b/explorer/interpreter/action.h
index ddda48191d992..46851f4318633 100644
--- a/explorer/interpreter/action.h
+++ b/explorer/interpreter/action.h
@@ -18,7 +18,7 @@
 #include "explorer/ast/pattern.h"
 #include "explorer/ast/statement.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/source_location.h"
 #include "explorer/interpreter/dictionary.h"
 #include "explorer/interpreter/heap_allocation_interface.h"
 #include "explorer/interpreter/stack.h"
diff --git a/explorer/interpreter/action_stack.h b/explorer/interpreter/action_stack.h
index 587c7c19d8230..5f70fd7ce589d 100644
--- a/explorer/interpreter/action_stack.h
+++ b/explorer/interpreter/action_stack.h
@@ -12,7 +12,7 @@
 #include "common/ostream.h"
 #include "explorer/ast/statement.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/trace_stream.h"
 #include "explorer/interpreter/action.h"
 
 namespace Carbon {
diff --git a/explorer/interpreter/builtins.cpp b/explorer/interpreter/builtins.cpp
index f99f5c2760e6b..579ac6817f81d 100644
--- a/explorer/interpreter/builtins.cpp
+++ b/explorer/interpreter/builtins.cpp
@@ -4,7 +4,7 @@
 
 #include "explorer/interpreter/builtins.h"
 
-#include "explorer/common/error_builders.h"
+#include "explorer/base/error_builders.h"
 
 using llvm::dyn_cast;
 
diff --git a/explorer/interpreter/builtins.h b/explorer/interpreter/builtins.h
index 180ae271d741b..d983ac1c63fde 100644
--- a/explorer/interpreter/builtins.h
+++ b/explorer/interpreter/builtins.h
@@ -14,8 +14,8 @@
 #include "explorer/ast/declaration.h"
 #include "explorer/ast/expression.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/nonnull.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/nonnull.h"
+#include "explorer/base/source_location.h"
 
 namespace Carbon {
 
diff --git a/explorer/interpreter/dictionary.h b/explorer/interpreter/dictionary.h
index 7f3dbb2b53494..487fdccbd313e 100644
--- a/explorer/interpreter/dictionary.h
+++ b/explorer/interpreter/dictionary.h
@@ -8,7 +8,7 @@
 #include <iterator>
 #include <optional>
 
-#include "explorer/common/arena.h"
+#include "explorer/base/arena.h"
 
 namespace Carbon {
 
diff --git a/explorer/interpreter/exec_program.cpp b/explorer/interpreter/exec_program.cpp
index 26570b7478497..21bf90fef77ad 100644
--- a/explorer/interpreter/exec_program.cpp
+++ b/explorer/interpreter/exec_program.cpp
@@ -9,8 +9,8 @@
 #include "common/check.h"
 #include "common/error.h"
 #include "common/ostream.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/trace_stream.h"
 #include "explorer/interpreter/interpreter.h"
 #include "explorer/interpreter/resolve_control_flow.h"
 #include "explorer/interpreter/resolve_names.h"
diff --git a/explorer/interpreter/exec_program.h b/explorer/interpreter/exec_program.h
index 12998d2c0cb69..959663501cc0d 100644
--- a/explorer/interpreter/exec_program.h
+++ b/explorer/interpreter/exec_program.h
@@ -10,7 +10,7 @@
 #define CARBON_EXPLORER_INTERPRETER_EXEC_PROGRAM_H_
 
 #include "explorer/ast/ast.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/trace_stream.h"
 #include "llvm/Support/raw_ostream.h"
 
 namespace Carbon {
diff --git a/explorer/interpreter/heap.cpp b/explorer/interpreter/heap.cpp
index 92975e39f2336..2a35e8d59dabb 100644
--- a/explorer/interpreter/heap.cpp
+++ b/explorer/interpreter/heap.cpp
@@ -7,8 +7,8 @@
 #include "common/check.h"
 #include "common/error.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/error_builders.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/error_builders.h"
+#include "explorer/base/source_location.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/Error.h"
 
diff --git a/explorer/interpreter/heap.h b/explorer/interpreter/heap.h
index d701639c1053b..13ef47f4be6a1 100644
--- a/explorer/interpreter/heap.h
+++ b/explorer/interpreter/heap.h
@@ -11,9 +11,9 @@
 #include "explorer/ast/address.h"
 #include "explorer/ast/value.h"
 #include "explorer/ast/value_node.h"
-#include "explorer/common/nonnull.h"
-#include "explorer/common/source_location.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/nonnull.h"
+#include "explorer/base/source_location.h"
+#include "explorer/base/trace_stream.h"
 #include "explorer/interpreter/heap_allocation_interface.h"
 
 namespace Carbon {
diff --git a/explorer/interpreter/heap_allocation_interface.h b/explorer/interpreter/heap_allocation_interface.h
index 84ece4ca9ed2b..01bd76bcaddb4 100644
--- a/explorer/interpreter/heap_allocation_interface.h
+++ b/explorer/interpreter/heap_allocation_interface.h
@@ -8,9 +8,9 @@
 #include "common/error.h"
 #include "explorer/ast/address.h"
 #include "explorer/ast/value_node.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/nonnull.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/nonnull.h"
+#include "explorer/base/source_location.h"
 
 namespace Carbon {
 
diff --git a/explorer/interpreter/interpreter.cpp b/explorer/interpreter/interpreter.cpp
index 9592b889815e3..e967b8d27fb8c 100644
--- a/explorer/interpreter/interpreter.cpp
+++ b/explorer/interpreter/interpreter.cpp
@@ -22,10 +22,10 @@
 #include "explorer/ast/expression.h"
 #include "explorer/ast/expression_category.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/error_builders.h"
-#include "explorer/common/source_location.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/error_builders.h"
+#include "explorer/base/source_location.h"
+#include "explorer/base/trace_stream.h"
 #include "explorer/interpreter/action.h"
 #include "explorer/interpreter/action_stack.h"
 #include "explorer/interpreter/pattern_match.h"
diff --git a/explorer/interpreter/interpreter.h b/explorer/interpreter/interpreter.h
index b312ca00e0756..3b5f4f9596279 100644
--- a/explorer/interpreter/interpreter.h
+++ b/explorer/interpreter/interpreter.h
@@ -15,7 +15,7 @@
 #include "explorer/ast/expression.h"
 #include "explorer/ast/pattern.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/trace_stream.h"
 #include "explorer/interpreter/action.h"
 #include "explorer/interpreter/heap.h"
 #include "llvm/ADT/ArrayRef.h"
diff --git a/explorer/interpreter/matching_impl_set.cpp b/explorer/interpreter/matching_impl_set.cpp
index e902e0e64f3cd..a3b2bf4dac2bb 100644
--- a/explorer/interpreter/matching_impl_set.cpp
+++ b/explorer/interpreter/matching_impl_set.cpp
@@ -6,9 +6,9 @@
 #include "common/error.h"
 #include "explorer/ast/declaration.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/error_builders.h"
-#include "explorer/common/nonnull.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/error_builders.h"
+#include "explorer/base/nonnull.h"
+#include "explorer/base/source_location.h"
 #include "explorer/interpreter/type_checker.h"
 
 namespace Carbon {
diff --git a/explorer/interpreter/matching_impl_set.h b/explorer/interpreter/matching_impl_set.h
index 886a84a22cde2..de80ce341f4a3 100644
--- a/explorer/interpreter/matching_impl_set.h
+++ b/explorer/interpreter/matching_impl_set.h
@@ -10,7 +10,7 @@
 #include "common/ostream.h"
 #include "explorer/ast/declaration.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/nonnull.h"
+#include "explorer/base/nonnull.h"
 #include "explorer/interpreter/impl_scope.h"
 #include "llvm/ADT/DenseMap.h"
 
diff --git a/explorer/interpreter/pattern_analysis.h b/explorer/interpreter/pattern_analysis.h
index 85d6c81ebf33b..378f68d5e2c55 100644
--- a/explorer/interpreter/pattern_analysis.h
+++ b/explorer/interpreter/pattern_analysis.h
@@ -9,7 +9,7 @@
 
 #include "explorer/ast/pattern.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/nonnull.h"
+#include "explorer/base/nonnull.h"
 #include "llvm/ADT/PointerUnion.h"
 
 namespace Carbon {
diff --git a/explorer/interpreter/pattern_match.cpp b/explorer/interpreter/pattern_match.cpp
index 30166fc78b4e6..96c32c8e09336 100644
--- a/explorer/interpreter/pattern_match.cpp
+++ b/explorer/interpreter/pattern_match.cpp
@@ -5,8 +5,8 @@
 #include "explorer/interpreter/pattern_match.h"
 
 #include "explorer/ast/value.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/trace_stream.h"
 #include "explorer/interpreter/action.h"
 #include "llvm/Support/Casting.h"
 
diff --git a/explorer/interpreter/pattern_match.h b/explorer/interpreter/pattern_match.h
index ef54c66455c46..a97aeb820402b 100644
--- a/explorer/interpreter/pattern_match.h
+++ b/explorer/interpreter/pattern_match.h
@@ -9,8 +9,8 @@
 
 #include "explorer/ast/bindings.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/nonnull.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/nonnull.h"
+#include "explorer/base/source_location.h"
 
 namespace Carbon {
 
diff --git a/explorer/interpreter/resolve_control_flow.cpp b/explorer/interpreter/resolve_control_flow.cpp
index 94e722d558608..a0ac58cb46780 100644
--- a/explorer/interpreter/resolve_control_flow.cpp
+++ b/explorer/interpreter/resolve_control_flow.cpp
@@ -7,7 +7,7 @@
 #include "explorer/ast/declaration.h"
 #include "explorer/ast/return_term.h"
 #include "explorer/ast/statement.h"
-#include "explorer/common/error_builders.h"
+#include "explorer/base/error_builders.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Error.h"
 
diff --git a/explorer/interpreter/resolve_control_flow.h b/explorer/interpreter/resolve_control_flow.h
index 09ee8eccbd78e..1ff461f2b1c9a 100644
--- a/explorer/interpreter/resolve_control_flow.h
+++ b/explorer/interpreter/resolve_control_flow.h
@@ -6,8 +6,8 @@
 #define CARBON_EXPLORER_INTERPRETER_RESOLVE_CONTROL_FLOW_H_
 
 #include "explorer/ast/ast.h"
-#include "explorer/common/nonnull.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/nonnull.h"
+#include "explorer/base/trace_stream.h"
 
 namespace Carbon {
 
diff --git a/explorer/interpreter/resolve_names.h b/explorer/interpreter/resolve_names.h
index 7b8be2510db31..8e231df8e17a5 100644
--- a/explorer/interpreter/resolve_names.h
+++ b/explorer/interpreter/resolve_names.h
@@ -6,8 +6,8 @@
 #define CARBON_EXPLORER_INTERPRETER_RESOLVE_NAMES_H_
 
 #include "explorer/ast/ast.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/trace_stream.h"
 
 namespace Carbon {
 
diff --git a/explorer/interpreter/resolve_unformed.cpp b/explorer/interpreter/resolve_unformed.cpp
index ab2e248c8eb7b..b9bd2bdcea84c 100644
--- a/explorer/interpreter/resolve_unformed.cpp
+++ b/explorer/interpreter/resolve_unformed.cpp
@@ -10,7 +10,7 @@
 #include "explorer/ast/ast.h"
 #include "explorer/ast/expression.h"
 #include "explorer/ast/pattern.h"
-#include "explorer/common/nonnull.h"
+#include "explorer/base/nonnull.h"
 #include "explorer/interpreter/stack_space.h"
 
 using llvm::cast;
diff --git a/explorer/interpreter/resolve_unformed.h b/explorer/interpreter/resolve_unformed.h
index 4b9caa36f2564..f572b4ded37b5 100644
--- a/explorer/interpreter/resolve_unformed.h
+++ b/explorer/interpreter/resolve_unformed.h
@@ -9,8 +9,8 @@
 #include <unordered_map>
 
 #include "explorer/ast/ast.h"
-#include "explorer/common/nonnull.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/nonnull.h"
+#include "explorer/base/trace_stream.h"
 
 namespace Carbon {
 
diff --git a/explorer/interpreter/type_checker.cpp b/explorer/interpreter/type_checker.cpp
index 3e522e6d295e5..fac635065b12a 100644
--- a/explorer/interpreter/type_checker.cpp
+++ b/explorer/interpreter/type_checker.cpp
@@ -22,10 +22,10 @@
 #include "explorer/ast/pattern.h"
 #include "explorer/ast/value.h"
 #include "explorer/ast/value_transform.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/error_builders.h"
-#include "explorer/common/source_location.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/error_builders.h"
+#include "explorer/base/source_location.h"
+#include "explorer/base/trace_stream.h"
 #include "explorer/interpreter/impl_scope.h"
 #include "explorer/interpreter/interpreter.h"
 #include "explorer/interpreter/pattern_analysis.h"
diff --git a/explorer/interpreter/type_checker.h b/explorer/interpreter/type_checker.h
index 6945440fb686f..ce52ffa8e9e1f 100644
--- a/explorer/interpreter/type_checker.h
+++ b/explorer/interpreter/type_checker.h
@@ -18,8 +18,8 @@
 #include "explorer/ast/expression.h"
 #include "explorer/ast/statement.h"
 #include "explorer/ast/value.h"
-#include "explorer/common/nonnull.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/nonnull.h"
+#include "explorer/base/trace_stream.h"
 #include "explorer/interpreter/builtins.h"
 #include "explorer/interpreter/dictionary.h"
 #include "explorer/interpreter/impl_scope.h"
diff --git a/explorer/interpreter/type_structure.h b/explorer/interpreter/type_structure.h
index bfa365178b7d9..862fb7b152dba 100644
--- a/explorer/interpreter/type_structure.h
+++ b/explorer/interpreter/type_structure.h
@@ -8,7 +8,7 @@
 #include <vector>
 
 #include "common/ostream.h"
-#include "explorer/common/nonnull.h"
+#include "explorer/base/nonnull.h"
 #include "llvm/Support/Compiler.h"
 
 namespace Carbon {
diff --git a/explorer/interpreter/type_utils.h b/explorer/interpreter/type_utils.h
index e951e56f0f089..37367d42a943f 100644
--- a/explorer/interpreter/type_utils.h
+++ b/explorer/interpreter/type_utils.h
@@ -5,7 +5,7 @@
 #ifndef CARBON_EXPLORER_INTERPRETER_TYPE_UTILS_H_
 #define CARBON_EXPLORER_INTERPRETER_TYPE_UTILS_H_
 
-#include "explorer/common/nonnull.h"
+#include "explorer/base/nonnull.h"
 
 namespace Carbon {
 
diff --git a/explorer/main.cpp b/explorer/main.cpp
index ead23a2166c19..3d70c6b8dea9d 100644
--- a/explorer/main.cpp
+++ b/explorer/main.cpp
@@ -15,7 +15,7 @@
 #include <vector>
 
 #include "common/error.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/trace_stream.h"
 #include "explorer/parse_and_execute/parse_and_execute.h"
 #include "llvm/ADT/ScopeExit.h"
 #include "llvm/ADT/SmallString.h"
diff --git a/explorer/parse_and_execute/BUILD b/explorer/parse_and_execute/BUILD
index e9f7276306a46..9638c8686566c 100644
--- a/explorer/parse_and_execute/BUILD
+++ b/explorer/parse_and_execute/BUILD
@@ -14,7 +14,7 @@ cc_library(
     deps = [
         "//common:check",
         "//common:error",
-        "//explorer/common:trace_stream",
+        "//explorer/base:trace_stream",
         "//explorer/interpreter:exec_program",
         "//explorer/interpreter:stack_space",
         "//explorer/syntax",
diff --git a/explorer/parse_and_execute/parse_and_execute.cpp b/explorer/parse_and_execute/parse_and_execute.cpp
index a1a8a39f0ebca..16cdb24e49fd6 100644
--- a/explorer/parse_and_execute/parse_and_execute.cpp
+++ b/explorer/parse_and_execute/parse_and_execute.cpp
@@ -7,7 +7,7 @@
 #include <locale>
 
 #include "common/error.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/trace_stream.h"
 #include "explorer/interpreter/exec_program.h"
 #include "explorer/interpreter/stack_space.h"
 #include "explorer/syntax/parse.h"
diff --git a/explorer/parse_and_execute/parse_and_execute.h b/explorer/parse_and_execute/parse_and_execute.h
index d31eae6edbd31..28cc3a14b091f 100644
--- a/explorer/parse_and_execute/parse_and_execute.h
+++ b/explorer/parse_and_execute/parse_and_execute.h
@@ -6,7 +6,7 @@
 #define CARBON_EXPLORER_PARSE_AND_EXECUTE_PARSE_AND_EXECUTE_H_
 
 #include "common/error.h"
-#include "explorer/common/trace_stream.h"
+#include "explorer/base/trace_stream.h"
 #include "llvm/Support/VirtualFileSystem.h"
 
 namespace Carbon {
diff --git a/explorer/syntax/BUILD b/explorer/syntax/BUILD
index 9efc2771c36e5..fc3369dc3d6e9 100644
--- a/explorer/syntax/BUILD
+++ b/explorer/syntax/BUILD
@@ -15,7 +15,7 @@ cc_test(
     srcs = ["parse_test.cpp"],
     deps = [
         ":syntax",
-        "//explorer/common:arena",
+        "//explorer/base:arena",
         "//testing/util:gtest_main",
         "@com_google_googletest//:gtest",
     ],
@@ -42,8 +42,8 @@ cc_library(
         ":syntax",
         "//common:error",
         "//explorer/ast",
-        "//explorer/common:arena",
-        "//explorer/common:nonnull",
+        "//explorer/base:arena",
+        "//explorer/base:nonnull",
         "@llvm-project//llvm:Support",
     ],
 )
@@ -86,10 +86,10 @@ cc_library(
         "//explorer/ast",
         "//explorer/ast:expression_category",
         "//explorer/ast:paren_contents",
-        "//explorer/common:arena",
-        "//explorer/common:error_builders",
-        "//explorer/common:nonnull",
-        "//explorer/common:source_location",
+        "//explorer/base:arena",
+        "//explorer/base:error_builders",
+        "//explorer/base:nonnull",
+        "//explorer/base:source_location",
         "@llvm-project//llvm:Support",
     ],
 )
diff --git a/explorer/syntax/parse.cpp b/explorer/syntax/parse.cpp
index c7d13948e389c..51472e0f99200 100644
--- a/explorer/syntax/parse.cpp
+++ b/explorer/syntax/parse.cpp
@@ -6,7 +6,7 @@
 
 #include "common/check.h"
 #include "common/error.h"
-#include "explorer/common/error_builders.h"
+#include "explorer/base/error_builders.h"
 #include "explorer/syntax/lexer.h"
 #include "explorer/syntax/parse_and_lex_context.h"
 #include "explorer/syntax/parser.h"
diff --git a/explorer/syntax/parse.h b/explorer/syntax/parse.h
index b0ff5816366c4..623cac3119e17 100644
--- a/explorer/syntax/parse.h
+++ b/explorer/syntax/parse.h
@@ -9,8 +9,8 @@
 #include <variant>
 
 #include "explorer/ast/ast.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/source_location.h"
 #include "llvm/Support/VirtualFileSystem.h"
 
 namespace Carbon {
diff --git a/explorer/syntax/parse_and_lex_context.cpp b/explorer/syntax/parse_and_lex_context.cpp
index 914cddc68f120..ad31415dc0d29 100644
--- a/explorer/syntax/parse_and_lex_context.cpp
+++ b/explorer/syntax/parse_and_lex_context.cpp
@@ -4,7 +4,7 @@
 
 #include "explorer/syntax/parse_and_lex_context.h"
 
-#include "explorer/common/error_builders.h"
+#include "explorer/base/error_builders.h"
 
 namespace Carbon {
 
diff --git a/explorer/syntax/parse_and_lex_context.h b/explorer/syntax/parse_and_lex_context.h
index 6c5551bb2863d..5aa5fed2e20b1 100644
--- a/explorer/syntax/parse_and_lex_context.h
+++ b/explorer/syntax/parse_and_lex_context.h
@@ -8,7 +8,7 @@
 #include <variant>
 
 #include "explorer/ast/ast.h"
-#include "explorer/common/source_location.h"
+#include "explorer/base/source_location.h"
 #include "explorer/syntax/parser.h"  // from parser.ypp
 
 namespace Carbon {
diff --git a/explorer/syntax/parse_test.cpp b/explorer/syntax/parse_test.cpp
index ca8f0db408302..8588de59fb359 100644
--- a/explorer/syntax/parse_test.cpp
+++ b/explorer/syntax/parse_test.cpp
@@ -10,7 +10,7 @@
 #include <string>
 #include <variant>
 
-#include "explorer/common/arena.h"
+#include "explorer/base/arena.h"
 
 namespace Carbon::Testing {
 namespace {
diff --git a/explorer/syntax/parser.ypp b/explorer/syntax/parser.ypp
index d1b310129fe4d..df93d329180e3 100644
--- a/explorer/syntax/parser.ypp
+++ b/explorer/syntax/parser.ypp
@@ -74,8 +74,8 @@
   #include "explorer/ast/expression_category.h"
   #include "explorer/ast/paren_contents.h"
   #include "explorer/ast/pattern.h"
-  #include "explorer/common/arena.h"
-  #include "explorer/common/nonnull.h"
+  #include "explorer/base/arena.h"
+  #include "explorer/base/nonnull.h"
   #include "explorer/syntax/bison_wrap.h"
 
   namespace Carbon {
diff --git a/explorer/syntax/prelude.h b/explorer/syntax/prelude.h
index d17ecb5a4a35b..1843c7ef81461 100644
--- a/explorer/syntax/prelude.h
+++ b/explorer/syntax/prelude.h
@@ -8,8 +8,8 @@
 #include <string_view>
 
 #include "explorer/ast/declaration.h"
-#include "explorer/common/arena.h"
-#include "explorer/common/nonnull.h"
+#include "explorer/base/arena.h"
+#include "explorer/base/nonnull.h"
 #include "llvm/Support/VirtualFileSystem.h"
 
 namespace Carbon {