diff --git a/src/main/java/com/google/devtools/build/lib/bazel/bzlmod/Module.java b/src/main/java/com/google/devtools/build/lib/bazel/bzlmod/Module.java
index e20608c1b2d1de..61f44dc131d48e 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/bzlmod/Module.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/bzlmod/Module.java
@@ -73,6 +73,19 @@ public final String getCanonicalRepoName() {
    */
   public abstract int getCompatibilityLevel();
 
+  /**
+   * Target patterns identifying execution platforms to register when this module is selected. Note
+   * that these are what was written in module files verbatim, and don't contain canonical repo
+   * names.
+   */
+  public abstract ImmutableList<String> getExecutionPlatformsToRegister();
+
+  /**
+   * Target patterns identifying toolchains to register when this module is selected. Note that
+   * these are what was written in module files verbatim, and don't contain canonical repo names.
+   */
+  public abstract ImmutableList<String> getToolchainsToRegister();
+
   /**
    * The direct dependencies of this module. The key type is the repo name of the dep, and the value
    * type is the ModuleKey (name+version) of the dep.
@@ -125,7 +138,9 @@ public static Builder builder() {
         .setName("")
         .setVersion(Version.EMPTY)
         .setKey(ModuleKey.ROOT)
-        .setCompatibilityLevel(0);
+        .setCompatibilityLevel(0)
+        .setExecutionPlatformsToRegister(ImmutableList.of())
+        .setToolchainsToRegister(ImmutableList.of());
   }
 
   /**
@@ -153,6 +168,12 @@ public abstract static class Builder {
     /** Optional; defaults to {@code 0}. */
     public abstract Builder setCompatibilityLevel(int value);
 
+    /** Optional; defaults to an empty list. */
+    public abstract Builder setExecutionPlatformsToRegister(ImmutableList<String> value);
+
+    /** Optional; defaults to an empty list. */
+    public abstract Builder setToolchainsToRegister(ImmutableList<String> value);
+
     public abstract Builder setDeps(ImmutableMap<String, ModuleKey> value);
 
     abstract ImmutableMap.Builder<String, ModuleKey> depsBuilder();
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleFileGlobals.java b/src/main/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleFileGlobals.java
index 3bb56c75dc89ea..ef7ed904084e64 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleFileGlobals.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleFileGlobals.java
@@ -122,12 +122,38 @@ private void addRepoNameUsage(String repoName, String how, Location where) throw
             named = true,
             positional = false,
             defaultValue = "0"),
+        @Param(
+            name = "execution_platforms_to_register",
+            doc =
+                "A list of already-defined execution platforms to be registered when this module is"
+                    + " selected. Should be a list of absolute target patterns (ie. beginning with"
+                    + " either <code>@</code> or <code>//</code>). See <a"
+                    + " href=\"../../toolchains.html\">toolchain resolution</a> for more"
+                    + " information.",
+            named = true,
+            positional = false,
+            allowedTypes = {@ParamType(type = Iterable.class, generic1 = String.class)},
+            defaultValue = "[]"),
+        @Param(
+            name = "toolchains_to_register",
+            doc =
+                "A list of already-defined toolchains to be registered when this module is"
+                    + " selected. Should be a list of absolute target patterns (ie. beginning with"
+                    + " either <code>@</code> or <code>//</code>). See <a"
+                    + " href=\"../../toolchains.html\">toolchain resolution</a> for more"
+                    + " information.",
+            named = true,
+            positional = false,
+            allowedTypes = {@ParamType(type = Iterable.class, generic1 = String.class)},
+            defaultValue = "[]"),
       },
       useStarlarkThread = true)
   public void module(
       String name,
       String version,
       StarlarkInt compatibilityLevel,
+      Iterable<?> executionPlatformsToRegister,
+      Iterable<?> toolchainsToRegister,
       StarlarkThread thread)
       throws EvalException {
     if (moduleCalled) {
@@ -144,10 +170,29 @@ public void module(
     module
         .setName(name)
         .setVersion(parsedVersion)
-        .setCompatibilityLevel(compatibilityLevel.toInt("compatibility_level"));
+        .setCompatibilityLevel(compatibilityLevel.toInt("compatibility_level"))
+        .setExecutionPlatformsToRegister(
+            checkAllAbsolutePatterns(
+                executionPlatformsToRegister, "execution_platforms_to_register"))
+        .setToolchainsToRegister(
+            checkAllAbsolutePatterns(toolchainsToRegister, "toolchains_to_register"));
     addRepoNameUsage(name, "as the current module name", thread.getCallerLocation());
   }
 
+  private static ImmutableList<String> checkAllAbsolutePatterns(Iterable<?> iterable, String where)
+      throws EvalException {
+    Sequence<String> list = Sequence.cast(iterable, String.class, where);
+    for (String item : list) {
+      if (!item.startsWith("//") && !item.startsWith("@")) {
+        throw Starlark.errorf(
+            "Expected absolute target patterns (must begin with '//' or '@') for '%s' argument, but"
+                + " got '%s' as an argument",
+            where, item);
+      }
+    }
+    return list.getImmutableList();
+  }
+
   @StarlarkMethod(
       name = "bazel_dep",
       doc = "Declares a direct dependency on another Bazel module.",
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredExecutionPlatformsFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredExecutionPlatformsFunction.java
index 107620bb5bd0bc..60d6ca23b26575 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredExecutionPlatformsFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredExecutionPlatformsFunction.java
@@ -24,7 +24,8 @@
 import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
 import com.google.devtools.build.lib.analysis.platform.PlatformInfo;
 import com.google.devtools.build.lib.analysis.platform.PlatformProviderUtils;
-import com.google.devtools.build.lib.bazel.bzlmod.ExternalDepsException;
+import com.google.devtools.build.lib.bazel.bzlmod.BazelModuleResolutionValue;
+import com.google.devtools.build.lib.bazel.bzlmod.Module;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
@@ -34,6 +35,7 @@
 import com.google.devtools.build.lib.packages.Package;
 import com.google.devtools.build.lib.packages.Target;
 import com.google.devtools.build.lib.pkgcache.FilteringPolicy;
+import com.google.devtools.build.lib.rules.repository.RepositoryDelegatorFunction;
 import com.google.devtools.build.lib.server.FailureDetails.Analysis;
 import com.google.devtools.build.lib.server.FailureDetails.Analysis.Code;
 import com.google.devtools.build.lib.server.FailureDetails.FailureDetail;
@@ -96,6 +98,13 @@ public SkyValue compute(SkyKey skyKey, Environment env)
       }
     }
 
+    // Get registered execution platforms from bzlmod.
+    ImmutableList<TargetPattern> bzlmodExecutionPlatforms = getBzlmodExecutionPlatforms(env);
+    if (bzlmodExecutionPlatforms == null) {
+      return null;
+    }
+    targetPatternBuilder.addAll(TargetPatternUtil.toSigned(bzlmodExecutionPlatforms));
+
     // Get the registered execution platforms from the WORKSPACE.
     ImmutableList<TargetPattern> workspaceExecutionPlatforms = getWorkspaceExecutionPlatforms(env);
     if (workspaceExecutionPlatforms == null) {
@@ -146,6 +155,36 @@ public static ImmutableList<TargetPattern> getWorkspaceExecutionPlatforms(Enviro
     return externalPackage.getRegisteredExecutionPlatforms();
   }
 
+  @Nullable
+  private static ImmutableList<TargetPattern> getBzlmodExecutionPlatforms(Environment env)
+      throws InterruptedException, RegisteredExecutionPlatformsFunctionException {
+    if (!RepositoryDelegatorFunction.ENABLE_BZLMOD.get(env)) {
+      return ImmutableList.of();
+    }
+    BazelModuleResolutionValue bazelModuleResolutionValue =
+        (BazelModuleResolutionValue) env.getValue(BazelModuleResolutionValue.KEY);
+    if (bazelModuleResolutionValue == null) {
+      return null;
+    }
+    ImmutableList.Builder<TargetPattern> executionPlatforms = ImmutableList.builder();
+    for (Module module : bazelModuleResolutionValue.getDepGraph().values()) {
+      TargetPattern.Parser parser =
+          new TargetPattern.Parser(
+              PathFragment.EMPTY_FRAGMENT,
+              RepositoryName.createFromValidStrippedName(module.getCanonicalRepoName()),
+              bazelModuleResolutionValue.getFullRepoMapping(module.getKey()));
+      for (String pattern : module.getExecutionPlatformsToRegister()) {
+        try {
+          executionPlatforms.add(parser.parse(pattern));
+        } catch (TargetParsingException e) {
+          throw new RegisteredExecutionPlatformsFunctionException(
+              new InvalidExecutionPlatformLabelException(pattern, e), Transience.PERSISTENT);
+        }
+      }
+    }
+    return executionPlatforms.build();
+  }
+
   private static ImmutableList<ConfiguredTargetKey> configureRegisteredExecutionPlatforms(
       Environment env, BuildConfiguration configuration, List<Label> labels)
       throws InterruptedException, RegisteredExecutionPlatformsFunctionException {
@@ -246,10 +285,5 @@ private RegisteredExecutionPlatformsFunctionException(
         InvalidPlatformException cause, Transience transience) {
       super(cause, transience);
     }
-
-    private RegisteredExecutionPlatformsFunctionException(
-        ExternalDepsException cause, Transience transience) {
-      super(cause, transience);
-    }
   }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunction.java
index bd33592260db3a..d22fe776f78518 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunction.java
@@ -24,7 +24,9 @@
 import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
 import com.google.devtools.build.lib.analysis.platform.DeclaredToolchainInfo;
 import com.google.devtools.build.lib.analysis.platform.PlatformProviderUtils;
+import com.google.devtools.build.lib.bazel.bzlmod.BazelModuleResolutionValue;
 import com.google.devtools.build.lib.bazel.bzlmod.ExternalDepsException;
+import com.google.devtools.build.lib.bazel.bzlmod.Module;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
@@ -33,6 +35,7 @@
 import com.google.devtools.build.lib.cmdline.TargetPattern;
 import com.google.devtools.build.lib.packages.Package;
 import com.google.devtools.build.lib.pkgcache.FilteringPolicies;
+import com.google.devtools.build.lib.rules.repository.RepositoryDelegatorFunction;
 import com.google.devtools.build.lib.server.FailureDetails.Toolchain.Code;
 import com.google.devtools.build.lib.skyframe.TargetPatternUtil.InvalidTargetPatternException;
 import com.google.devtools.build.lib.vfs.PathFragment;
@@ -85,6 +88,13 @@ public SkyValue compute(SkyKey skyKey, Environment env)
           new InvalidToolchainLabelException(e), Transience.PERSISTENT);
     }
 
+    // Get registered toolchains from bzlmod.
+    ImmutableList<TargetPattern> bzlmodToolchains = getBzlmodToolchains(env);
+    if (bzlmodToolchains == null) {
+      return null;
+    }
+    targetPatternBuilder.addAll(TargetPatternUtil.toSigned(bzlmodToolchains));
+
     // Get the registered toolchains from the WORKSPACE.
     ImmutableList<TargetPattern> workspaceToolchains = getWorkspaceToolchains(env);
     if (workspaceToolchains == null) {
@@ -135,6 +145,36 @@ public static ImmutableList<TargetPattern> getWorkspaceToolchains(Environment en
     return externalPackage.getRegisteredToolchains();
   }
 
+  @Nullable
+  private static ImmutableList<TargetPattern> getBzlmodToolchains(Environment env)
+      throws InterruptedException, RegisteredToolchainsFunctionException {
+    if (!RepositoryDelegatorFunction.ENABLE_BZLMOD.get(env)) {
+      return ImmutableList.of();
+    }
+    BazelModuleResolutionValue bazelModuleResolutionValue =
+        (BazelModuleResolutionValue) env.getValue(BazelModuleResolutionValue.KEY);
+    if (bazelModuleResolutionValue == null) {
+      return null;
+    }
+    ImmutableList.Builder<TargetPattern> toolchains = ImmutableList.builder();
+    for (Module module : bazelModuleResolutionValue.getDepGraph().values()) {
+      TargetPattern.Parser parser =
+          new TargetPattern.Parser(
+              PathFragment.EMPTY_FRAGMENT,
+              RepositoryName.createFromValidStrippedName(module.getCanonicalRepoName()),
+              bazelModuleResolutionValue.getFullRepoMapping(module.getKey()));
+      for (String pattern : module.getToolchainsToRegister()) {
+        try {
+          toolchains.add(parser.parse(pattern));
+        } catch (TargetParsingException e) {
+          throw new RegisteredToolchainsFunctionException(
+              new InvalidToolchainLabelException(pattern, e), Transience.PERSISTENT);
+        }
+      }
+    }
+    return toolchains.build();
+  }
+
   private static ImmutableList<DeclaredToolchainInfo> configureRegisteredToolchains(
       Environment env, BuildConfiguration configuration, List<Label> labels)
       throws InterruptedException, RegisteredToolchainsFunctionException {
diff --git a/src/test/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleFileFunctionTest.java b/src/test/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleFileFunctionTest.java
index 8e7530b3095899..c6cb50a815b75d 100644
--- a/src/test/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleFileFunctionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/bazel/bzlmod/ModuleFileFunctionTest.java
@@ -174,7 +174,13 @@ public void setup() throws Exception {
   public void testRootModule() throws Exception {
     scratch.file(
         rootDirectory.getRelative("MODULE.bazel").getPathString(),
-        "module(name='A',version='0.1',compatibility_level=4)",
+        "module(",
+        "    name='A',",
+        "    version='0.1',",
+        "    compatibility_level=4,",
+        "    toolchains_to_register=['//my:toolchain', '//my:toolchain2'],",
+        "    execution_platforms_to_register=['//my:platform', '//my:platform2'],",
+        ")",
         "bazel_dep(name='B',version='1.0')",
         "bazel_dep(name='C',version='2.0',repo_name='see')",
         "single_version_override(module_name='D',version='18')",
@@ -197,6 +203,9 @@ public void testRootModule() throws Exception {
                 .setVersion(Version.parse("0.1"))
                 .setKey(ModuleKey.ROOT)
                 .setCompatibilityLevel(4)
+                .setExecutionPlatformsToRegister(
+                    ImmutableList.of("//my:platform", "//my:platform2"))
+                .setToolchainsToRegister(ImmutableList.of("//my:toolchain", "//my:toolchain2"))
                 .addDep("B", createModuleKey("B", "1.0"))
                 .addDep("see", createModuleKey("C", "2.0"))
                 .build());
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/RegisteredExecutionPlatformsFunctionTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/RegisteredExecutionPlatformsFunctionTest.java
index 89b96b536b9e41..196466d6467b17 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/RegisteredExecutionPlatformsFunctionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/RegisteredExecutionPlatformsFunctionTest.java
@@ -15,6 +15,7 @@
 package com.google.devtools.build.lib.skyframe;
 
 import static com.google.common.truth.Truth.assertThat;
+import static com.google.devtools.build.lib.bazel.bzlmod.BzlmodTestUtil.createModuleKey;
 import static com.google.devtools.build.skyframe.EvaluationResultSubjectFactory.assertThatEvaluationResult;
 import static org.junit.Assert.assertThrows;
 
@@ -23,16 +24,22 @@
 import com.google.common.truth.IterableSubject;
 import com.google.devtools.build.lib.analysis.ViewCreationFailedException;
 import com.google.devtools.build.lib.analysis.platform.ConstraintCollection;
+import com.google.devtools.build.lib.bazel.bzlmod.FakeRegistry;
+import com.google.devtools.build.lib.bazel.bzlmod.ModuleFileFunction;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
 import com.google.devtools.build.lib.rules.platform.ToolchainTestCase;
 import com.google.devtools.build.lib.skyframe.PlatformLookupUtil.InvalidPlatformException;
+import com.google.devtools.build.lib.skyframe.PrecomputedValue.Injected;
 import com.google.devtools.build.lib.skyframe.util.SkyframeExecutorTestUtils;
+import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.skyframe.EvaluationResult;
 import com.google.devtools.build.skyframe.SkyKey;
+import java.io.IOException;
 import java.util.List;
 import java.util.stream.Collectors;
 import javax.annotation.Nullable;
+import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -44,6 +51,9 @@
 @RunWith(JUnit4.class)
 public class RegisteredExecutionPlatformsFunctionTest extends ToolchainTestCase {
 
+  private Path moduleRoot;
+  private FakeRegistry registry;
+
   protected EvaluationResult<RegisteredExecutionPlatformsValue>
       requestExecutionPlatformsFromSkyframe(SkyKey executionPlatformsKey)
           throws InterruptedException {
@@ -79,6 +89,30 @@ protected static List<Label> collectExecutionPlatformLabels(
         .collect(Collectors.toList());
   }
 
+  @Override
+  protected boolean enableBzlmod() {
+    return true;
+  }
+
+  @Override
+  protected ImmutableList<Injected> extraPrecomputedValues() {
+    try {
+      moduleRoot = scratch.dir("modules");
+    } catch (IOException e) {
+      throw new IllegalStateException(e);
+    }
+    registry = FakeRegistry.DEFAULT_FACTORY.newFakeRegistry(moduleRoot.getPathString());
+    return ImmutableList.of(
+        PrecomputedValue.injected(
+            ModuleFileFunction.REGISTRIES, ImmutableList.of(registry.getUrl())),
+        PrecomputedValue.injected(ModuleFileFunction.IGNORE_DEV_DEPS, false));
+  }
+
+  @Before
+  public void setUpForBzlmod() throws Exception {
+    scratch.file("MODULE.bazel");
+  }
+
   @Test
   public void testRegisteredExecutionPlatforms() throws Exception {
     // Request the executionPlatforms.
@@ -299,6 +333,77 @@ public void testRegisteredExecutionPlatforms_reload() throws Exception {
         .contains(Label.parseAbsoluteUnchecked("//platform:execution_platform_2"));
   }
 
+  @Test
+  public void testRegisteredExecutionPlatforms_bzlmod() throws Exception {
+    scratch.overwriteFile(
+        "MODULE.bazel",
+        "module(execution_platforms_to_register=['//:plat'])",
+        "bazel_dep(name='B',version='1.0')",
+        "bazel_dep(name='C',version='1.1')");
+    registry
+        .addModule(
+            createModuleKey("B", "1.0"),
+            "module(",
+            "    name='B',",
+            "    version='1.0',",
+            "    execution_platforms_to_register=['//:plat'],",
+            ")",
+            "bazel_dep(name='D',version='1.0')")
+        .addModule(
+            createModuleKey("C", "1.1"),
+            "module(",
+            "    name='C',",
+            "    version='1.1',",
+            "    execution_platforms_to_register=['//:plat'],",
+            ")",
+            "bazel_dep(name='D',version='1.1')")
+        // D@1.0 is not selected
+        .addModule(
+            createModuleKey("D", "1.0"),
+            "module(",
+            "    name='D',",
+            "    version='1.0',",
+            "    execution_platforms_to_register=['//:plat'],",
+            ")")
+        .addModule(
+            createModuleKey("D", "1.1"),
+            "module(",
+            "    name='D',",
+            "    version='1.1',",
+            "    execution_platforms_to_register=['@E//:plat', '//:plat'],",
+            ")",
+            "bazel_dep(name='E',version='1.0')")
+        .addModule(createModuleKey("E", "1.0"), "module(name='E', version='1.0')");
+    for (String repo : ImmutableList.of("B.1.0", "C.1.1", "D.1.0", "D.1.1", "E.1.0")) {
+      scratch.file(moduleRoot.getRelative(repo).getRelative("WORKSPACE").getPathString());
+      scratch.file(
+          moduleRoot.getRelative(repo).getRelative("BUILD").getPathString(),
+          "platform(name='plat')");
+    }
+    scratch.overwriteFile("BUILD", "platform(name='plat');platform(name='wsplat')");
+    rewriteWorkspace("register_execution_platforms('//:wsplat')");
+
+    SkyKey executionPlatformsKey = RegisteredExecutionPlatformsValue.key(targetConfigKey);
+    EvaluationResult<RegisteredExecutionPlatformsValue> result =
+        requestExecutionPlatformsFromSkyframe(executionPlatformsKey);
+    if (result.hasError()) {
+      throw result.getError().getException();
+    }
+    assertThatEvaluationResult(result).hasNoError();
+
+    // Verify that the execution platforms registered with bzlmod come in the BFS order and before
+    // WORKSPACE registrations.
+    assertExecutionPlatformLabels(result.get(executionPlatformsKey))
+        .containsExactly(
+            Label.parseAbsoluteUnchecked("//:plat"),
+            Label.parseAbsoluteUnchecked("@B.1.0//:plat"),
+            Label.parseAbsoluteUnchecked("@C.1.1//:plat"),
+            Label.parseAbsoluteUnchecked("@E.1.0//:plat"),
+            Label.parseAbsoluteUnchecked("@D.1.1//:plat"),
+            Label.parseAbsoluteUnchecked("//:wsplat"))
+        .inOrder();
+  }
+
   @Test
   public void testRegisteredExecutionPlatformsValue_equalsAndHashCode()
       throws ConstraintCollection.DuplicateConstraintException {
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunctionTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunctionTest.java
index 71d59c77cabfb9..64b916de24081e 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunctionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunctionTest.java
@@ -15,18 +15,25 @@
 package com.google.devtools.build.lib.skyframe;
 
 import static com.google.common.truth.Truth.assertThat;
+import static com.google.devtools.build.lib.bazel.bzlmod.BzlmodTestUtil.createModuleKey;
 import static com.google.devtools.build.skyframe.EvaluationResultSubjectFactory.assertThatEvaluationResult;
 
 import com.google.common.collect.ImmutableList;
 import com.google.common.testing.EqualsTester;
 import com.google.devtools.build.lib.analysis.platform.DeclaredToolchainInfo;
 import com.google.devtools.build.lib.analysis.platform.ToolchainTypeInfo;
+import com.google.devtools.build.lib.bazel.bzlmod.FakeRegistry;
+import com.google.devtools.build.lib.bazel.bzlmod.ModuleFileFunction;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
 import com.google.devtools.build.lib.rules.platform.ToolchainTestCase;
+import com.google.devtools.build.lib.skyframe.PrecomputedValue.Injected;
+import com.google.devtools.build.lib.vfs.Path;
 import com.google.devtools.build.skyframe.EvaluationResult;
 import com.google.devtools.build.skyframe.SkyKey;
+import java.io.IOException;
 import java.util.stream.Collectors;
+import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -35,6 +42,33 @@
 @RunWith(JUnit4.class)
 public class RegisteredToolchainsFunctionTest extends ToolchainTestCase {
 
+  private Path moduleRoot;
+  private FakeRegistry registry;
+
+  @Override
+  protected boolean enableBzlmod() {
+    return true;
+  }
+
+  @Override
+  protected ImmutableList<Injected> extraPrecomputedValues() {
+    try {
+      moduleRoot = scratch.dir("modules");
+    } catch (IOException e) {
+      throw new IllegalStateException(e);
+    }
+    registry = FakeRegistry.DEFAULT_FACTORY.newFakeRegistry(moduleRoot.getPathString());
+    return ImmutableList.of(
+        PrecomputedValue.injected(
+            ModuleFileFunction.REGISTRIES, ImmutableList.of(registry.getUrl())),
+        PrecomputedValue.injected(ModuleFileFunction.IGNORE_DEV_DEPS, false));
+  }
+
+  @Before
+  public void setUpForBzlmod() throws Exception {
+    scratch.file("MODULE.bazel");
+  }
+
   @Test
   public void testRegisteredToolchains() throws Exception {
     // Request the toolchains.
@@ -264,6 +298,115 @@ public void testRegisteredToolchains_reload() throws Exception {
         .contains(Label.parseAbsoluteUnchecked("//toolchain:toolchain_2_impl"));
   }
 
+  @Test
+  public void testRegisteredToolchains_bzlmod() throws Exception {
+    scratch.overwriteFile(
+        "MODULE.bazel",
+        "module(toolchains_to_register=['//:tool'])",
+        "bazel_dep(name='B',version='1.0')",
+        "bazel_dep(name='C',version='1.1')",
+        "bazel_dep(name='toolchain_def',version='1.0')");
+    registry
+        .addModule(
+            createModuleKey("B", "1.0"),
+            "module(",
+            "    name='B',",
+            "    version='1.0',",
+            "    toolchains_to_register=['//:tool'],",
+            ")",
+            "bazel_dep(name='D',version='1.0')",
+            "bazel_dep(name='toolchain_def',version='1.0')")
+        .addModule(
+            createModuleKey("C", "1.1"),
+            "module(",
+            "    name='C',",
+            "    version='1.1',",
+            "    toolchains_to_register=['//:tool'],",
+            ")",
+            "bazel_dep(name='D',version='1.1')",
+            "bazel_dep(name='toolchain_def',version='1.0')")
+        // D@1.0 is not selected
+        .addModule(
+            createModuleKey("D", "1.0"),
+            "module(",
+            "    name='D',",
+            "    version='1.0',",
+            "    toolchains_to_register=['//:tool'],",
+            ")",
+            "bazel_dep(name='toolchain_def',version='1.0')")
+        .addModule(
+            createModuleKey("D", "1.1"),
+            "module(",
+            "    name='D',",
+            "    version='1.1',",
+            "    toolchains_to_register=['@E//:tool', '//:tool'],",
+            ")",
+            "bazel_dep(name='E',version='1.0')",
+            "bazel_dep(name='toolchain_def',version='1.0')")
+        .addModule(
+            createModuleKey("E", "1.0"),
+            "module(name='E',version='1.0')",
+            "bazel_dep(name='toolchain_def',version='1.0')")
+        .addModule(
+            createModuleKey("toolchain_def", "1.0"), "module(name='toolchain_def',version='1.0')");
+
+    // Everyone depends on toolchain_def@1.0 for the declare_toolchain macro.
+    Path toolchainDefDir = moduleRoot.getRelative("toolchain_def.1.0");
+    scratch.file(toolchainDefDir.getRelative("WORKSPACE").getPathString());
+    scratch.file(
+        toolchainDefDir.getRelative("BUILD").getPathString(),
+        "toolchain_type(name = 'test_toolchain')");
+    scratch.file(
+        toolchainDefDir.getRelative("toolchain_def.bzl").getPathString(),
+        "def _impl(ctx):",
+        "    toolchain = platform_common.ToolchainInfo(data = ctx.attr.data)",
+        "    return [toolchain]",
+        "test_toolchain = rule(implementation = _impl, attrs = {'data': attr.string()})",
+        "def declare_toolchain(name):",
+        "    native.toolchain(",
+        "        name = name,",
+        "        toolchain_type = Label('//:test_toolchain'),",
+        "        toolchain = ':' + name + '_impl')",
+        "    test_toolchain(",
+        "        name = name + '_impl',",
+        "        data = 'stuff')");
+
+    // Now create the toolchains for each module.
+    for (String repo : ImmutableList.of("B.1.0", "C.1.1", "D.1.0", "D.1.1", "E.1.0")) {
+      scratch.file(moduleRoot.getRelative(repo).getRelative("WORKSPACE").getPathString());
+      scratch.file(
+          moduleRoot.getRelative(repo).getRelative("BUILD").getPathString(),
+          "load('@toolchain_def//:toolchain_def.bzl', 'declare_toolchain')",
+          "declare_toolchain(name='tool')");
+    }
+    scratch.overwriteFile(
+        "BUILD",
+        "load('@toolchain_def//:toolchain_def.bzl', 'declare_toolchain')",
+        "declare_toolchain(name='tool')",
+        "declare_toolchain(name='wstool')");
+    rewriteWorkspace("register_toolchains('//:wstool')");
+
+    SkyKey toolchainsKey = RegisteredToolchainsValue.key(targetConfigKey);
+    EvaluationResult<RegisteredToolchainsValue> result =
+        requestToolchainsFromSkyframe(toolchainsKey);
+    if (result.hasError()) {
+      throw result.getError().getException();
+    }
+    assertThatEvaluationResult(result).hasNoError();
+
+    // Verify that the toolchains registered with bzlmod come in the BFS order and before WORKSPACE
+    // registrations.
+    assertToolchainLabels(result.get(toolchainsKey))
+        .containsAtLeast(
+            Label.parseAbsoluteUnchecked("//:tool_impl"),
+            Label.parseAbsoluteUnchecked("@B.1.0//:tool_impl"),
+            Label.parseAbsoluteUnchecked("@C.1.1//:tool_impl"),
+            Label.parseAbsoluteUnchecked("@E.1.0//:tool_impl"),
+            Label.parseAbsoluteUnchecked("@D.1.1//:tool_impl"),
+            Label.parseAbsoluteUnchecked("//:wstool_impl"))
+        .inOrder();
+  }
+
   @Test
   public void testRegisteredToolchainsValue_equalsAndHashCode() throws Exception {
     DeclaredToolchainInfo toolchain1 =