diff --git a/spec/spectator/mocks/mock_spec.cr b/spec/spectator/mocks/mock_spec.cr
new file mode 100644
index 0000000..6ca3dda
--- /dev/null
+++ b/spec/spectator/mocks/mock_spec.cr
@@ -0,0 +1,44 @@
+require "../../spec_helper"
+
+Spectator.describe Spectator::Mock do
+  describe "#define_subclass" do
+    class Thing
+      def method1
+        42
+      end
+
+      def method2
+        :original
+      end
+
+      def method3
+        "original"
+      end
+    end
+
+    Spectator::Mock.define_subclass(Thing, MockThing, :mock_name, method1: 123) do
+      stub def method2
+        :stubbed
+      end
+    end
+
+    let(thing) { MockThing.new }
+
+    it "defines a subclass of the mocked type" do
+      expect(MockThing).to be_lt(Thing)
+    end
+
+    it "overrides responses from methods with keyword arguments" do
+      expect(thing.method1).to eq(123)
+    end
+
+    it "overrides responses from methods defined in the block" do
+      expect(thing.method2).to eq(:stubbed)
+    end
+
+    it "allows methods to be stubbed" do
+      stub = Spectator::ValueStub.new(:method3, "stubbed")
+      expect { thing._spectator_define_stub(stub) }.to change { thing.method3 }.from("original").to("stubbed")
+    end
+  end
+end
diff --git a/src/spectator/mocks/mock.cr b/src/spectator/mocks/mock.cr
new file mode 100644
index 0000000..f4c2f16
--- /dev/null
+++ b/src/spectator/mocks/mock.cr
@@ -0,0 +1,47 @@
+require "./method_call"
+require "./mocked"
+require "./stub"
+require "./stubbed_name"
+require "./value_stub"
+
+module Spectator
+  module Mock
+    macro define_subclass(mocked_type, type_name, name = nil, **value_methods, &block)
+      {% if name %}@[::Spectator::StubbedName({{name}})]{% end %}
+      class {{type_name.id}} < {{mocked_type.id}}
+        include ::Spectator::Mocked
+
+        {% begin %}
+          @_spectator_stubs = [
+            {% for key, value in value_methods %}
+              ::Spectator::ValueStub.new({{key.id.symbolize}}, {{value}}),
+            {% end %}
+          ] of ::Spectator::Stub
+        {% end %}
+
+        def _spectator_define_stub(stub : ::Spectator::Stub) : Nil
+          @_spectator_stubs.unshift(stub)
+        end
+
+        def _spectator_find_stub(call : ::Spectator::MethodCall) : ::Spectator::Stub?
+          @_spectator_stubs.find &.===(call)
+        end
+
+        # Returns the mock's name formatted for user output.
+        private def _spectator_stubbed_name : String
+          \{% if anno = @type.annotation(::Spectator::StubbedName) %}
+            "#<Mock {{mocked_type.id}} \"" + \{{(anno[0] || :Anonymous.id).stringify}} + "\">"
+          \{% else %}
+            "#<Mock {{mocked_type.id}}>"
+          \{% end %}
+        end
+
+        macro finished
+          stub_all {{mocked_type.id}}
+        end
+
+        {% if block %}{{block.body}}{% end %}
+      end
+    end
+  end
+end
diff --git a/src/spectator/mocks/mocked.cr b/src/spectator/mocks/mocked.cr
new file mode 100644
index 0000000..c7f9205
--- /dev/null
+++ b/src/spectator/mocks/mocked.cr
@@ -0,0 +1,52 @@
+require "./method_call"
+require "./stubbable"
+
+module Spectator
+  module Mocked
+    include Stubbable
+
+    # Method called when a stub isn't found.
+    #
+    # The received message is captured in *call*.
+    # Yield to call the original method's implementation.
+    # The stubbed method returns the value returned by this method.
+    # This method can also raise an error if it's impossible to return something.
+    def _spectator_stub_fallback(call : MethodCall, &)
+      raise "oof"
+    end
+
+    # Method called when a stub isn't found.
+    #
+    # The received message is captured in *call*.
+    # The expected return type is provided by *type*.
+    # Yield to call the original method's implementation.
+    # The stubbed method returns the value returned by this method.
+    # This method can also raise an error if it's impossible to return something.
+    def _spectator_stub_fallback(call : MethodCall, type, &)
+      raise "oof"
+    end
+
+    # Method called when a stub isn't found.
+    #
+    # This is similar to `#_spectator_stub_fallback`,
+    # but called when the original (un-stubbed) method isn't available.
+    # The received message is captured in *call*.
+    # The stubbed method returns the value returned by this method.
+    # This method can also raise an error if it's impossible to return something.
+    def _spectator_abstract_stub_fallback(call : MethodCall)
+      raise "oof"
+    end
+
+    # Method called when a stub isn't found.
+    #
+    # This is similar to `#_spectator_stub_fallback`,
+    # but called when the original (un-stubbed) method isn't available.
+    # The received message is captured in *call*.
+    # The expected return type is provided by *type*.
+    # The stubbed method returns the value returned by this method.
+    # This method can also raise an error if it's impossible to return something.
+    def _spectator_abstract_stub_fallback(call : MethodCall, type)
+      raise "oof"
+    end
+  end
+end