diff --git a/lib/phoenix_html/form.ex b/lib/phoenix_html/form.ex
index 794252d..67e8c8b 100644
--- a/lib/phoenix_html/form.ex
+++ b/lib/phoenix_html/form.ex
@@ -64,6 +64,7 @@ defmodule Phoenix.HTML.Form do
             id: nil,
             name: nil,
             data: nil,
+            action: nil,
             hidden: [],
             params: %{},
             errors: [],
@@ -74,6 +75,7 @@ defmodule Phoenix.HTML.Form do
           source: Phoenix.HTML.FormData.t(),
           name: String.t(),
           data: %{field => term},
+          action: atom(),
           params: %{binary => term},
           hidden: Keyword.t(),
           options: Keyword.t(),
@@ -191,18 +193,32 @@ defmodule Phoenix.HTML.Form do
   @doc """
   Receives two forms structs and checks if the given field changed.
 
-  The field will have changed if either its associated value or errors
-  changed. This is mostly used for optimization engines as an extension
-  of the `Access` behaviour.
+  The field will have changed if either its associated value, errors,
+  action, or implementation changed. This is mostly used for optimization
+  engines as an extension of the `Access` behaviour.
   """
   @spec input_changed?(t, t, field()) :: boolean()
   def input_changed?(
-        %Form{impl: impl1, id: id1, name: name1, errors: errors1, source: source1} = form1,
-        %Form{impl: impl2, id: id2, name: name2, errors: errors2, source: source2} = form2,
+        %Form{
+          impl: impl1,
+          id: id1,
+          name: name1,
+          errors: errors1,
+          source: source1,
+          action: action1
+        } = form1,
+        %Form{
+          impl: impl2,
+          id: id2,
+          name: name2,
+          errors: errors2,
+          source: source2,
+          action: action2
+        } = form2,
         field
       )
       when is_atom(field) or is_binary(field) do
-    impl1 != impl2 or id1 != id2 or name1 != name2 or
+    impl1 != impl2 or id1 != id2 or name1 != name2 or action1 != action2 or
       field_errors(errors1, field) != field_errors(errors2, field) or
       impl1.input_value(source1, form1, field) != impl2.input_value(source2, form2, field)
   end
diff --git a/lib/phoenix_html/form_data.ex b/lib/phoenix_html/form_data.ex
index 02eec75..0efc546 100644
--- a/lib/phoenix_html/form_data.ex
+++ b/lib/phoenix_html/form_data.ex
@@ -56,6 +56,8 @@ defprotocol Phoenix.HTML.FormData do
       applies if the field value is a list and no parameters were
       sent through the form.
 
+    * `:action` - The user defined action being taken by the form, such
+      as `:validate`, `:save`, etc.
   """
   @spec to_form(t, Phoenix.HTML.Form.t(), Phoenix.HTML.Form.field(), Keyword.t()) ::
           [Phoenix.HTML.Form.t()]
@@ -79,6 +81,7 @@ defimpl Phoenix.HTML.FormData, for: Map do
   def to_form(conn_or_atom_or_map, opts) do
     {name, params, opts} = name_params_and_opts(conn_or_atom_or_map, opts)
     {errors, opts} = Keyword.pop(opts, :errors, [])
+    {action, opts} = Keyword.pop(opts, :action, nil)
     id = Keyword.get(opts, :id) || name
 
     unless is_binary(id) or is_nil(id) do
@@ -93,6 +96,7 @@ defimpl Phoenix.HTML.FormData, for: Map do
       params: params,
       data: %{},
       errors: errors,
+      action: action,
       options: opts
     }
   end
@@ -118,6 +122,7 @@ defimpl Phoenix.HTML.FormData, for: Map do
     {name, opts} = Keyword.pop(opts, :as)
     {id, opts} = Keyword.pop(opts, :id)
     {hidden, opts} = Keyword.pop(opts, :hidden, [])
+    {action, opts} = Keyword.pop(opts, :action)
 
     id = to_string(id || form.id <> "_#{field}")
     name = to_string(name || form.name <> "[#{field}]")
@@ -133,6 +138,7 @@ defimpl Phoenix.HTML.FormData, for: Map do
             id: id,
             name: name,
             data: default,
+            action: action,
             params: params || %{},
             hidden: hidden,
             options: opts
@@ -157,6 +163,7 @@ defimpl Phoenix.HTML.FormData, for: Map do
             source: conn_or_atom_or_map,
             impl: __MODULE__,
             index: index,
+            action: action,
             id: id <> "_" <> index_string,
             name: name <> "[" <> index_string <> "]",
             data: data,
diff --git a/test/phoenix_html/form_test.exs b/test/phoenix_html/form_test.exs
index cb11c45..75fb40f 100644
--- a/test/phoenix_html/form_test.exs
+++ b/test/phoenix_html/form_test.exs
@@ -138,6 +138,12 @@ defmodule Phoenix.HTML.FormTest do
     assert input_changed?(form, form(%{"foo" => "bar"}), "foo")
   end
 
+  test "input_changed? with changed action or method" do
+    form = form(%{}, action: :validate)
+    refute input_changed?(form, %{form | action: :validate}, :foo)
+    assert input_changed?(form, %{form | action: :save}, :foo)
+  end
+
   describe "access" do
     test "without name and atom keys" do
       form =