diff --git a/lib/inngest/error.ex b/lib/inngest/error.ex
index 4e3505a..79ff1b5 100644
--- a/lib/inngest/error.ex
+++ b/lib/inngest/error.ex
@@ -21,3 +21,7 @@ end
 defmodule Inngest.ConcurrencyConfigError do
   defexception [:message]
 end
+
+defmodule Inngest.IdempotencyConfigError do
+  defexception [:message]
+end
diff --git a/lib/inngest/function.ex b/lib/inngest/function.ex
index c391302..a660659 100644
--- a/lib/inngest/function.ex
+++ b/lib/inngest/function.ex
@@ -168,31 +168,27 @@ defmodule Inngest.Function do
           |> maybe_debounce()
           |> maybe_batch_events()
           |> maybe_rate_limit()
+          |> maybe_idempotency()
           |> maybe_concurrency()
         ] ++ handler
       end
 
       defp retries(), do: fn_opts() |> Map.get(:retries)
 
-      defp maybe_debounce(config) do
-        fn_opts()
-        |> Inngest.FnOpts.validate_debounce(config)
-      end
+      defp maybe_debounce(config),
+        do: fn_opts() |> Inngest.FnOpts.validate_debounce(config)
 
-      defp maybe_batch_events(config) do
-        fn_opts()
-        |> Inngest.FnOpts.validate_batch_events(config)
-      end
+      defp maybe_batch_events(config),
+        do: fn_opts() |> Inngest.FnOpts.validate_batch_events(config)
 
-      defp maybe_rate_limit(config) do
-        fn_opts()
-        |> Inngest.FnOpts.validate_rate_limit(config)
-      end
+      defp maybe_rate_limit(config),
+        do: fn_opts() |> Inngest.FnOpts.validate_rate_limit(config)
 
-      defp maybe_concurrency(config) do
-        fn_opts()
-        |> Inngest.FnOpts.validate_concurrency(config)
-      end
+      defp maybe_idempotency(config),
+        do: fn_opts() |> Inngest.FnOpts.validate_idempotency(config)
+
+      defp maybe_concurrency(config),
+        do: fn_opts() |> Inngest.FnOpts.validate_concurrency(config)
 
       defp fn_opts() do
         case __MODULE__.__info__(:attributes) |> Keyword.get(:func) |> List.first() do
diff --git a/lib/inngest/function/config.ex b/lib/inngest/function/config.ex
index 22685ff..a45ae06 100644
--- a/lib/inngest/function/config.ex
+++ b/lib/inngest/function/config.ex
@@ -9,6 +9,7 @@ defmodule Inngest.FnOpts do
     :debounce,
     :batch_events,
     :rate_limit,
+    :idempotency,
     :concurrency,
     retries: 3
   ]
@@ -22,6 +23,7 @@ defmodule Inngest.FnOpts do
           debounce: debounce() | nil,
           batch_events: batch_events() | nil,
           rate_limit: rate_limit() | nil,
+          idempotency: idempotency() | nil,
           concurrency: concurrency() | nil
         }
 
@@ -41,6 +43,8 @@ defmodule Inngest.FnOpts do
           key: binary() | nil
         }
 
+  @type idempotency() :: binary()
+
   @type concurrency() ::
           number()
           | concurrency_option()
@@ -54,7 +58,7 @@ defmodule Inngest.FnOpts do
   @concurrency_scopes ["fn", "env", "account"]
 
   @doc """
-  Validate the debounce configuration
+  Validate the debounce settings
   """
   @spec validate_debounce(t(), map()) :: map()
   def validate_debounce(fnopts, config) do
@@ -86,7 +90,7 @@ defmodule Inngest.FnOpts do
   end
 
   @doc """
-  Validate the event batch config
+  Validate the event batch settings
   """
   @spec validate_batch_events(t(), map()) :: map()
   def validate_batch_events(fnopts, config) do
@@ -121,7 +125,7 @@ defmodule Inngest.FnOpts do
   end
 
   @doc """
-  Validate the rate limit config
+  Validate the rate limit settings
   """
   @spec validate_rate_limit(t(), map()) :: map()
   def validate_rate_limit(fnopts, config) do
@@ -155,7 +159,25 @@ defmodule Inngest.FnOpts do
   end
 
   @doc """
-  Validate the concurrency config
+  Validate the idempotency settings
+  """
+  def validate_idempotency(fnopts, config) do
+    # NOTE: nothing really to validate, just have this for the sake of consistency
+    case fnopts |> Map.get(:idempotency) do
+      nil ->
+        config
+
+      setting ->
+        if !is_binary(setting) do
+          raise Inngest.IdempotencyConfigError, message: "idempotency must be a CEL string"
+        end
+
+        Map.put(config, :idempotency, setting)
+    end
+  end
+
+  @doc """
+  Validate the concurrency settings
   """
   @spec validate_concurrency(t(), map()) :: map()
   def validate_concurrency(fnopts, config) do
diff --git a/test/inngest/function/cases/idempotency_test.exs b/test/inngest/function/cases/idempotency_test.exs
new file mode 100644
index 0000000..93a8a01
--- /dev/null
+++ b/test/inngest/function/cases/idempotency_test.exs
@@ -0,0 +1,53 @@
+defmodule Inngest.Function.Cases.IdempotencyTest do
+  use ExUnit.Case, async: true
+
+  alias Inngest.Test.DevServer
+  import Inngest.Test.Helper
+
+  @default_sleep 3_000
+
+  @tag :integration
+  test "should only run 1 out of 10" do
+    event_ids =
+      Enum.map(1..10, fn _ -> send_test_event("test/plug.idempotency", %{foobar: false}) end)
+
+    Process.sleep(@default_sleep)
+
+    fn_runs =
+      event_ids
+      |> Enum.map(fn id ->
+        {:ok, %{"data" => data}} = DevServer.run_ids(id)
+
+        if Enum.count(data) == 1 do
+          assert [
+                   %{
+                     "output" => "Done",
+                     "status" => "Completed",
+                     "run_id" => run_id
+                   }
+                 ] = data
+
+          run_id
+        else
+          nil
+        end
+      end)
+      |> Enum.filter(&(!is_nil(&1)))
+
+    assert Enum.count(fn_runs) == 1
+
+    # sending with a different value will run
+    other = send_test_event("test/plug.idempotency", %{foobar: "hello"})
+    Process.sleep(@default_sleep)
+
+    assert {:ok,
+            %{
+              "data" => [
+                %{
+                  "output" => "Done",
+                  "status" => "Completed"
+                }
+              ]
+            }} = DevServer.run_ids(other)
+  end
+end
diff --git a/test/inngest/function/cases/rate_limit_test.exs b/test/inngest/function/cases/rate_limit_test.exs
index f409223..64d046f 100644
--- a/test/inngest/function/cases/rate_limit_test.exs
+++ b/test/inngest/function/cases/rate_limit_test.exs
@@ -7,7 +7,7 @@ defmodule Inngest.Function.Cases.RateLimitTest do
   @default_sleep 10_000
 
   @tag :integration
-  test "should only run 2 out of 10" do
+  test "should <= 2 out of 10" do
     event_ids = Enum.map(1..10, fn _ -> send_test_event("test/plug.ratelimit") end)
 
     Process.sleep(@default_sleep)
@@ -25,6 +25,8 @@ defmodule Inngest.Function.Cases.RateLimitTest do
                      "run_id" => run_id
                    }
                  ] = data
+
+          run_id
         else
           nil
         end
diff --git a/test/inngest/function/config_test.exs b/test/inngest/function/config_test.exs
index 6e675dc..665c56d 100644
--- a/test/inngest/function/config_test.exs
+++ b/test/inngest/function/config_test.exs
@@ -167,6 +167,30 @@ defmodule Inngest.FnOptsTest do
     end
   end
 
+  describe "validate_idempotency/2" do
+    @fn_opts %FnOpts{
+      id: "foobar",
+      name: "Foobar",
+      idempotency: "event.data.foobar"
+    }
+
+    test "should succeed with valid settings" do
+      assert %{
+               idempotency: "event.data.foobar"
+             } = FnOpts.validate_idempotency(@fn_opts, @config)
+    end
+
+    test "should raise if value is not string" do
+      opts = %{@fn_opts | idempotency: false}
+
+      assert_raise Inngest.IdempotencyConfigError,
+                   "idempotency must be a CEL string",
+                   fn ->
+                     FnOpts.validate_idempotency(opts, @config)
+                   end
+    end
+  end
+
   describe "validate_concurrency/2" do
     @fn_opts %FnOpts{
       id: "foobar",
diff --git a/test/support/cases/concurrency_fn.ex b/test/support/cases/concurrency_fn.ex
index 24fbf6f..c535029 100644
--- a/test/support/cases/concurrency_fn.ex
+++ b/test/support/cases/concurrency_fn.ex
@@ -14,7 +14,6 @@ defmodule Inngest.Test.Case.ConcurrencyFn do
   @trigger %Trigger{event: "test/plug.throttle"}
 
   @impl true
-  @spec exec(any, %{:step => atom, optional(any) => any}) :: {:ok, <<_::72>>}
   def exec(ctx, %{step: step} = _args) do
     _ =
       step.run(ctx, "wait", fn ->
diff --git a/test/support/cases/idempotent_fn.ex b/test/support/cases/idempotent_fn.ex
new file mode 100644
index 0000000..85a193d
--- /dev/null
+++ b/test/support/cases/idempotent_fn.ex
@@ -0,0 +1,18 @@
+defmodule Inngest.Test.Case.IdempotentFn do
+  @moduledoc false
+
+  use Inngest.Function
+  alias Inngest.{FnOpts, Trigger}
+
+  @func %FnOpts{
+    id: "idempotent-fn",
+    name: "Idempotent Function",
+    idempotency: "event.data.foobar"
+  }
+  @trigger %Trigger{event: "test/plug.idempotency"}
+
+  @impl true
+  def exec(_ctx, _args) do
+    {:ok, "Done"}
+  end
+end