diff --git a/lib/livebook/runtime/erl_dist.ex b/lib/livebook/runtime/erl_dist.ex
index d0f780c94..1dd04daf8 100644
--- a/lib/livebook/runtime/erl_dist.ex
+++ b/lib/livebook/runtime/erl_dist.ex
@@ -26,6 +26,7 @@ defmodule Livebook.Runtime.ErlDist do
       Livebook.Runtime.Evaluator.Tracer,
       Livebook.Runtime.Evaluator.ObjectTracker,
       Livebook.Runtime.Evaluator.DefaultFormatter,
+      Livebook.Runtime.Evaluator.Doctests,
       Livebook.Intellisense,
       Livebook.Intellisense.Docs,
       Livebook.Intellisense.IdentifierMatcher,
diff --git a/lib/livebook/runtime/evaluator.ex b/lib/livebook/runtime/evaluator.ex
index 22007f91b..f9e3bc24f 100644
--- a/lib/livebook/runtime/evaluator.ex
+++ b/lib/livebook/runtime/evaluator.ex
@@ -32,7 +32,9 @@ defmodule Livebook.Runtime.Evaluator do
           runtime_broadcast_to: pid(),
           object_tracker: pid(),
           contexts: %{ref() => context()},
-          initial_context: context()
+          initial_context: context(),
+          initial_context_version: nil | (md5 :: binary()),
+          ignored_pdict_keys: list(term())
         }
 
   @typedoc """
@@ -376,6 +378,10 @@ defmodule Livebook.Runtime.Evaluator do
           {new_context, result, code_error, identifiers_used, identifiers_defined}
       end
 
+    if ebin_path() do
+      Livebook.Runtime.Evaluator.Doctests.run(new_context.env.context_modules)
+    end
+
     state = put_context(state, ref, new_context)
 
     Evaluator.IOProxy.flush(state.io_proxy)
@@ -404,16 +410,19 @@ defmodule Livebook.Runtime.Evaluator do
   defp handle_cast({:forget_evaluation, ref}, state) do
     {context, state} = pop_context(state, ref)
 
-    for module <- context.env.context_modules do
-      delete_module!(module)
+    if context do
+      for module <- context.env.context_modules do
+        delete_module!(module)
 
-      # And we immediately purge the newly deleted code
-      :code.purge(module)
+        # And we immediately purge the newly deleted code
+        :code.purge(module)
+      end
+
+      Evaluator.ObjectTracker.remove_reference_sync(state.object_tracker, {self(), ref})
+
+      :erlang.garbage_collect(self())
     end
 
-    Evaluator.ObjectTracker.remove_reference_sync(state.object_tracker, {self(), ref})
-
-    :erlang.garbage_collect(self())
     {:noreply, state}
   end
 
diff --git a/lib/livebook/runtime/evaluator/default_formatter.ex b/lib/livebook/runtime/evaluator/default_formatter.ex
index fa4266964..705f2f7eb 100644
--- a/lib/livebook/runtime/evaluator/default_formatter.ex
+++ b/lib/livebook/runtime/evaluator/default_formatter.ex
@@ -3,7 +3,7 @@ defmodule Livebook.Runtime.Evaluator.DefaultFormatter do
 
   # The formatter used by Livebook for rendering the results.
   #
-  # See `Livebook.Notebook.Cell` for available output formats.
+  # See `Livebook.Runtime.output/0` for available output formats.
 
   @behaviour Livebook.Runtime.Evaluator.Formatter
 
@@ -61,7 +61,7 @@ defmodule Livebook.Runtime.Evaluator.DefaultFormatter do
     end
   end
 
-  defp inspect_opts(opts \\ []) do
+  def inspect_opts(opts \\ []) do
     default_opts = [pretty: true, width: 100, syntax_colors: syntax_colors()]
     Keyword.merge(default_opts, opts)
   end
diff --git a/lib/livebook/runtime/evaluator/doctests.ex b/lib/livebook/runtime/evaluator/doctests.ex
new file mode 100644
index 000000000..41f12aaf7
--- /dev/null
+++ b/lib/livebook/runtime/evaluator/doctests.ex
@@ -0,0 +1,281 @@
+# TODO: remove the else branch when we require Elixir v1.14.2
+if Version.compare(System.version(), "1.14.2") != :lt do
+  defmodule Livebook.Runtime.Evaluator.Doctests do
+    @moduledoc false
+
+    @test_timeout 5_000
+    @line_width 80
+    @pad_size 3
+
+    @doc """
+    Runs doctests in the given modules.
+    """
+    @spec run(list(module())) :: :ok
+    def run(modules) do
+      case define_test_module(modules) do
+        {:ok, test_module} ->
+          if test_module.tests != [] do
+            tests =
+              test_module.tests
+              |> Enum.sort_by(& &1.tags.doctest_line)
+              |> Enum.map(&run_test/1)
+
+            formatted = format_results(tests)
+            put_output({:text, formatted})
+          end
+
+          delete_test_module(test_module)
+
+        {:error, kind, error} ->
+          IO.warn(Exception.format(kind, error, []), [])
+      end
+
+      :ok
+    end
+
+    defp define_test_module(modules) do
+      name = Module.concat([LivebookDoctest | modules])
+
+      try do
+        defmodule name do
+          use ExUnit.Case, register: false
+
+          for module <- modules do
+            doctest module
+          end
+        end
+
+        {:ok, name.__ex_unit__()}
+      catch
+        kind, error -> {:error, kind, error}
+      end
+    end
+
+    defp delete_test_module(%{name: module}) do
+      :code.delete(module)
+      :code.purge(module)
+    end
+
+    defp run_test(test) do
+      runner_pid = self()
+
+      {test_pid, test_ref} =
+        spawn_monitor(fn ->
+          test = exec_test(test)
+          send(runner_pid, {:test_finished, self(), test})
+        end)
+
+      receive_test_reply(test, test_pid, test_ref)
+    end
+
+    defp receive_test_reply(test, test_pid, test_ref) do
+      receive do
+        {:test_finished, ^test_pid, test} ->
+          Process.demonitor(test_ref, [:flush])
+          test
+
+        {:DOWN, ^test_ref, :process, ^test_pid, error} ->
+          %{test | state: failed({:EXIT, test_pid}, error, [])}
+      after
+        @test_timeout ->
+          case Process.info(test_pid, :current_stacktrace) do
+            {:current_stacktrace, stacktrace} ->
+              Process.exit(test_pid, :kill)
+
+              receive do
+                {:DOWN, ^test_ref, :process, ^test_pid, _} -> :ok
+              end
+
+              exception = RuntimeError.exception("doctest timed out after #{@test_timeout} ms")
+              %{test | state: failed(:error, exception, prune_stacktrace(stacktrace))}
+
+            nil ->
+              receive_test_reply(test, test_pid, test_ref)
+          end
+      end
+    end
+
+    defp exec_test(%ExUnit.Test{module: module, name: name} = test) do
+      apply(module, name, [:none])
+      test
+    catch
+      kind, error ->
+        %{test | state: failed(kind, error, prune_stacktrace(__STACKTRACE__))}
+    end
+
+    defp failed(kind, reason, stack) do
+      {:failed, {kind, Exception.normalize(kind, reason, stack), stack}}
+    end
+
+    # As soon as we see our runner module, we ignore the rest of the stacktrace
+    def prune_stacktrace([{__MODULE__, _, _, _} | _]), do: []
+    def prune_stacktrace([h | t]), do: [h | prune_stacktrace(t)]
+    def prune_stacktrace([]), do: []
+
+    # Formatting
+
+    defp format_results(tests) do
+      filed_tests = Enum.reject(tests, &(&1.state == nil))
+
+      test_count = length(tests)
+      failure_count = length(filed_tests)
+
+      doctests_pl = pluralize(test_count, "doctest", "doctests")
+      failures_pl = pluralize(failure_count, "failure", "failures")
+
+      headline =
+        colorize(
+          if(failure_count == 0, do: :green, else: :red),
+          "#{test_count} #{doctests_pl}, #{failure_count} #{failures_pl}"
+        )
+
+      failures =
+        for {test, idx} <- Enum.with_index(filed_tests) do
+          {:failed, failure} = test.state
+
+          name =
+            test.name
+            |> Atom.to_string()
+            |> String.replace(~r/ \(\d+\)$/, "")
+
+          line = test.tags.doctest_line
+
+          [
+            "\n\n",
+            "#{idx + 1}) #{name} (line #{line})\n",
+            format_failure(failure, test)
+          ]
+        end
+
+      IO.iodata_to_binary([headline, failures])
+    end
+
+    defp format_failure({:error, %ExUnit.AssertionError{} = reason, _stack}, _test) do
+      diff =
+        ExUnit.Formatter.format_assertion_diff(
+          reason,
+          @pad_size + 2,
+          @line_width,
+          &diff_formatter/2
+        )
+
+      expected = diff[:right]
+      got = diff[:left]
+
+      source = String.trim(reason.doctest)
+
+      [
+        String.duplicate(" ", @pad_size),
+        format_label("doctest"),
+        "\n",
+        pad(source, @pad_size + 2),
+        "\n",
+        String.duplicate(" ", @pad_size),
+        format_label("expected"),
+        "\n",
+        String.duplicate(" ", @pad_size + 2),
+        expected,
+        "\n",
+        String.duplicate(" ", @pad_size),
+        format_label("got"),
+        "\n",
+        String.duplicate(" ", @pad_size + 2),
+        got
+      ]
+    end
+
+    defp format_failure({kind, reason, stacktrace}, test) do
+      {blamed, stacktrace} = Exception.blame(kind, reason, stacktrace)
+
+      banner =
+        case blamed do
+          %FunctionClauseError{} ->
+            banner = Exception.format_banner(kind, reason, stacktrace)
+            inspect_opts = Livebook.Runtime.Evaluator.DefaultFormatter.inspect_opts()
+            blame = FunctionClauseError.blame(blamed, &inspect(&1, inspect_opts), &blame_match/1)
+            colorize(:red, banner) <> blame
+
+          _ ->
+            banner = Exception.format_banner(kind, blamed, stacktrace)
+            colorize(:red, banner)
+        end
+
+      if stacktrace == [] do
+        pad(banner, @pad_size)
+      else
+        [
+          pad(banner, @pad_size),
+          "\n",
+          String.duplicate(" ", @pad_size),
+          format_label("stacktrace"),
+          format_stacktrace(stacktrace, test.module, test.name)
+        ]
+      end
+    end
+
+    defp format_stacktrace(stacktrace, test_case, test) do
+      for entry <- stacktrace do
+        message = format_stacktrace_entry(entry, test_case, test)
+        "\n" <> pad(message, @pad_size + 2)
+      end
+    end
+
+    defp format_stacktrace_entry({test_case, test, _, location}, test_case, test) do
+      "doctest at line #{location[:line]}"
+    end
+
+    defp format_stacktrace_entry(entry, _test_case, _test) do
+      Exception.format_stacktrace_entry(entry)
+    end
+
+    defp format_label(label), do: colorize(:cyan, "#{label}:")
+
+    defp pad(string, pad_size) do
+      padding = String.duplicate(" ", pad_size)
+      padding <> String.replace(string, "\n", "\n" <> padding)
+    end
+
+    defp blame_match(%{match?: true, node: node}), do: Macro.to_string(node)
+
+    defp blame_match(%{match?: false, node: node}) do
+      colorize(:red, Macro.to_string(node))
+    end
+
+    defp diff_formatter(:diff_enabled?, _doc), do: true
+
+    defp diff_formatter(key, doc) do
+      colors = [
+        diff_delete: :red,
+        diff_delete_whitespace: IO.ANSI.color_background(4, 0, 0),
+        diff_insert: :green,
+        diff_insert_whitespace: IO.ANSI.color_background(0, 3, 0)
+      ]
+
+      Inspect.Algebra.color(doc, key, %Inspect.Opts{syntax_colors: colors})
+    end
+
+    defp colorize(color, string) do
+      [color, string, :reset]
+      |> IO.ANSI.format_fragment(true)
+      |> IO.iodata_to_binary()
+    end
+
+    defp pluralize(1, singular, _plural), do: singular
+    defp pluralize(_, _singular, plural), do: plural
+
+    defp put_output(output) do
+      gl = Process.group_leader()
+      ref = make_ref()
+
+      send(gl, {:io_request, self(), ref, {:livebook_put_output, output}})
+
+      receive do
+        {:io_reply, ^ref, reply} -> {:ok, reply}
+      end
+    end
+  end
+else
+  defmodule Livebook.Runtime.Evaluator.Doctests do
+    def run(_modules), do: :ok
+  end
+end
diff --git a/test/livebook/runtime/evaluator_test.exs b/test/livebook/runtime/evaluator_test.exs
index 4b6b85b00..70ae9d121 100644
--- a/test/livebook/runtime/evaluator_test.exs
+++ b/test/livebook/runtime/evaluator_test.exs
@@ -333,6 +333,55 @@ defmodule Livebook.Runtime.EvaluatorTest do
 
       assert {:docs_v1, _, _, _, _, _, _} = Code.fetch_docs(Livebook.Runtime.EvaluatorTest.Disk)
     end
+
+    @tag :with_ebin_path
+    test "runs doctests when a module is defined", %{evaluator: evaluator} do
+      code = ~S'''
+      defmodule Livebook.Runtime.EvaluatorTest.Doctests do
+        @doc """
+            iex> Livebook.Runtime.EvaluatorTest.Doctests.data()
+            %{
+              name: "Amy Santiago",
+              description: "nypd detective",
+              precinct: 99
+            }
+
+            iex> Livebook.Runtime.EvaluatorTest.Doctests.data()
+            %{name: "Jake Peralta", description: "NYPD detective"}
+        """
+        def data() do
+          %{
+            name: "Amy Santiago",
+            description: "nypd detective",
+            precinct: 99
+          }
+        end
+
+        @doc """
+            iex> Livebook.Runtime.EvaluatorTest.Doctests.raise_with_stacktrace()
+            :what
+        """
+        def raise_with_stacktrace() do
+          Enum.map(1, & &1)
+        end
+
+        @doc """
+            iex> Livebook.Runtime.EvaluatorTest.Doctests.exit()
+            :what
+        """
+        def exit() do
+          Process.exit(self(), :shutdown)
+        end
+      end
+      '''
+
+      Evaluator.evaluate_code(evaluator, code, :code_1, [])
+
+      assert_receive {:runtime_evaluation_output, :code_1, {:text, doctest_result}}
+      assert doctest_result =~ "4 doctests, 3 failures"
+
+      assert_receive {:runtime_evaluation_response, :code_1, {:ok, _}, metadata()}
+    end
   end
 
   describe "evaluate_code/6 identifier tracking" do