diff --git a/Makefile b/Makefile
index 55b5498f..506a5c53 100644
--- a/Makefile
+++ b/Makefile
@@ -40,7 +40,7 @@ clean:
 
 .PHONY: docs
 docs:
-	mix docs --open
+	mix docs -f html --open
 
 .PHONY: changelog
 changelog:
diff --git a/lib/inngest/function/input.ex b/lib/inngest/function/input.ex
index 3524eac8..828652e5 100644
--- a/lib/inngest/function/input.ex
+++ b/lib/inngest/function/input.ex
@@ -27,17 +27,15 @@ defmodule Inngest.Function.Context do
   """
 
   defstruct [
-    :attempt,
-    :run_id,
+    :middleware,
     # ETS table
     :index,
     steps: %{}
   ]
 
   @type t() :: %__MODULE__{
-          attempt: number(),
-          run_id: binary(),
           index: :ets.tid(),
-          steps: map()
+          steps: map(),
+          middleware: map()
         }
 end
diff --git a/lib/inngest/router/helper.ex b/lib/inngest/handler/helper.ex
similarity index 52%
rename from lib/inngest/router/helper.ex
rename to lib/inngest/handler/helper.ex
index 1d5587a3..5c5e4d06 100644
--- a/lib/inngest/router/helper.ex
+++ b/lib/inngest/handler/helper.ex
@@ -12,6 +12,15 @@ defmodule Inngest.Router.Helper do
     end
   end
 
+  def load_middleware(params) do
+    if Config.path_runtime_eval() do
+      %{middleware: middleware} = load_middleware_from_path(params)
+      middleware
+    else
+      Map.get(params, :middleware, [])
+    end
+  end
+
   @spec load_functions_from_path(map()) :: map()
   def load_functions_from_path(%{path: paths} = kv) when is_list(paths) do
     modules =
@@ -25,6 +34,28 @@ defmodule Inngest.Router.Helper do
     Map.put(kv, :funcs, modules)
   end
 
+  def load_functions_from_path(%{functions: funcs} = kv) when is_list(funcs) do
+    modules =
+      funcs
+      |> Enum.map(&Path.wildcard/1)
+      |> List.flatten()
+      |> Stream.filter(&(!File.dir?(&1)))
+      |> Enum.uniq()
+      |> extract_modules()
+
+    Map.put(kv, :funcs, modules)
+  end
+
+  def load_functions_from_path(%{functions: funcs} = kv) when is_binary(funcs) do
+    modules =
+      funcs
+      |> Path.wildcard()
+      |> Enum.filter(&(!File.dir?(&1)))
+      |> extract_modules()
+
+    Map.put(kv, :funcs, modules)
+  end
+
   def load_functions_from_path(%{path: path} = kv) when is_binary(path) do
     modules =
       path
@@ -37,6 +68,22 @@ defmodule Inngest.Router.Helper do
 
   def load_functions_from_path(kv), do: kv
 
+  @spec load_middleware_from_path(map()) :: map()
+  def load_middleware_from_path(%{middleware: middleware} = kv) when is_list(middleware) do
+    # modules =
+    #   middleware
+    #   |> IO.inspect()
+    #   |> Enum.map(&Path.wildcard/1)
+    #   |> List.flatten()
+    #   |> Stream.filter(&(!File.dir?(&1)))
+    #   |> Enum.uniq()
+    #   |> extract_modules()
+
+    Map.put(kv, :middleware, middleware)
+  end
+
+  def load_middleware_from_path(kv), do: kv
+
   defp extract_modules(files) do
     files
     |> Enum.flat_map(fn file ->
diff --git a/lib/inngest/router/invoke.ex b/lib/inngest/handler/invoke.ex
similarity index 81%
rename from lib/inngest/router/invoke.ex
rename to lib/inngest/handler/invoke.ex
index f7b0e2d4..a4362b02 100644
--- a/lib/inngest/router/invoke.ex
+++ b/lib/inngest/handler/invoke.ex
@@ -38,6 +38,27 @@ defmodule Inngest.Router.Invoke do
          %{private: %{raw_body: [body]}} = conn,
          %{"event" => event, "events" => events, "ctx" => ctx, "fnId" => fn_slug} = params
        ) do
+    input = %Inngest.Function.Input{
+      attempt: Map.get(ctx, "attempt", 0),
+      event: Inngest.Event.from(event),
+      events: Enum.map(events, &Inngest.Event.from/1),
+      run_id: Map.get(ctx, "run_id"),
+      step: Inngest.StepTool
+    }
+
+    # prepare steps to be passed into middlewares
+    steps =
+      case get_in(params, ["ctx", "stack", "stack"]) do
+        nil ->
+          []
+
+        stack ->
+          Enum.into(stack, [], fn hash ->
+            data = get_in(params, ["steps", hash])
+            %{id: hash, data: data}
+          end)
+      end
+
     func =
       params
       |> load_functions()
@@ -45,29 +66,41 @@ defmodule Inngest.Router.Invoke do
         Enum.member?(func.slugs(), fn_slug)
       end)
 
-    ctx = %Inngest.Function.Context{
-      attempt: Map.get(ctx, "attempt", 0),
-      run_id: Map.get(ctx, "run_id"),
-      steps: Map.get(params, "steps"),
-      index: :ets.new(:index, [:set, :private])
-    }
+    # Initialize middlewares
+    middleware =
+      params
+      |> load_middleware()
+      |> Enum.into(%{}, fn mid ->
+        arg = %{input: input, func: func, steps: steps}
+        opts = mid.init(arg)
+        {mid.name(), %{opts: opts, mid: mid}}
+      end)
 
-    input = %Inngest.Function.Input{
-      event: Inngest.Event.from(event),
-      events: Enum.map(events, &Inngest.Event.from/1),
-      run_id: Map.get(ctx, "run_id"),
-      step: Inngest.StepTool
+    # Transform inputs
+    steps =
+      steps
+      # TODO: Apply each middleware to the step data
+      # |> Stream.map(fn step ->
+      # end)
+      |> Enum.into(%{}, fn %{id: id, data: data} ->
+        {id, data}
+      end)
+
+    fnctx = %Inngest.Function.Context{
+      steps: steps,
+      middleware: middleware,
+      index: :ets.new(:index, [:set, :private])
     }
 
     resp =
       case Config.is_dev() do
         true ->
-          invoke(func, ctx, input)
+          invoke(func, fnctx, input)
 
         false ->
           with sig <- conn |> Plug.Conn.get_req_header(Headers.signature()) |> List.first(),
                true <- Signature.signing_key_valid?(sig, Config.signing_key(), body) do
-            invoke(func, ctx, input)
+            invoke(func, fnctx, input)
           else
             _ ->
               SdkResponse.from_result({:error, "unable to verify signature"}, retry: false)
diff --git a/lib/inngest/router/phoenix.ex b/lib/inngest/handler/phoenix.ex
similarity index 100%
rename from lib/inngest/router/phoenix.ex
rename to lib/inngest/handler/phoenix.ex
diff --git a/lib/inngest/router/plug.ex b/lib/inngest/handler/plug.ex
similarity index 95%
rename from lib/inngest/router/plug.ex
rename to lib/inngest/handler/plug.ex
index ee6abd41..4019cb5b 100644
--- a/lib/inngest/router/plug.ex
+++ b/lib/inngest/handler/plug.ex
@@ -22,6 +22,7 @@ defmodule Inngest.Router.Plug do
       end
       |> Enum.into(%{})
       |> Inngest.Router.Helper.load_functions_from_path()
+      |> Inngest.Router.Helper.load_middleware_from_path()
       |> Map.put(:framework, @framework)
       |> Macro.escape()
 
diff --git a/lib/inngest/router/register.ex b/lib/inngest/handler/register.ex
similarity index 100%
rename from lib/inngest/router/register.ex
rename to lib/inngest/handler/register.ex
diff --git a/lib/inngest/middleware.ex b/lib/inngest/middleware.ex
new file mode 100644
index 00000000..b09d5fc5
--- /dev/null
+++ b/lib/inngest/middleware.ex
@@ -0,0 +1,63 @@
+defmodule Inngest.Middleware do
+  @moduledoc """
+  Inngest Middleware specification
+  """
+
+  @type opts ::
+          binary()
+          | tuple()
+          | atom()
+          | integer()
+          | float()
+          | [opts]
+          | map()
+
+  @type init_args :: %{
+          input: Inngest.Function.Input,
+          func: Inngest.Function,
+          steps: list(map())
+        }
+
+  @type input_args :: %{
+          ctx: Inngest.Function.Input,
+          steps: list(map())
+        }
+
+  @type input_ret :: %{
+          ctx: Inngest.Function.Input,
+          steps: list(map())
+        }
+
+  @type output_args :: %{
+          result: %{data: any()},
+          step: Inngest.GeneratorOpCode.t() | nil
+        }
+
+  @type output_ret :: %{
+          result: %{data: any()}
+        }
+
+  @callback name() :: binary()
+
+  # NOTE: what to make available on init?
+  @callback init(init_args) :: opts
+
+  @callback transform_input(input_args, opts) :: input_ret
+
+  @callback transform_output(output_args, opts) :: output_ret
+
+  @callback before_memoization(opts) :: :ok
+
+  @callback after_memoization(opts) :: :ok
+
+  @callback before_execution(opts) :: :ok
+
+  @callback after_execution(opts) :: :ok
+
+  @optional_callbacks transform_input: 2,
+                      transform_output: 2,
+                      before_memoization: 1,
+                      after_memoization: 1,
+                      before_execution: 1,
+                      after_execution: 1
+end
diff --git a/test/support/cases/middleware/test.ex b/test/support/cases/middleware/test.ex
new file mode 100644
index 00000000..66014a5c
--- /dev/null
+++ b/test/support/cases/middleware/test.ex
@@ -0,0 +1,47 @@
+defmodule Inngest.Test.Case.Middleware.Test do
+  @moduledoc false
+
+  @behaviour Inngest.Middleware
+
+  @impl true
+  def init(_), do: []
+
+  @impl true
+  def name(), do: "test"
+
+  @impl true
+  def transform_input(input_args, _opts) do
+    IO.inspect("Transform input")
+    input_args
+  end
+
+  @impl true
+  def transform_output(output_args, _opts) do
+    IO.inspect("Transform outputx")
+    output_args
+  end
+
+  @impl true
+  def before_memoization(_opts) do
+    IO.inspect("Before memoization")
+    :ok
+  end
+
+  @impl true
+  def after_memoization(_opts) do
+    IO.inspect("After memoization")
+    :ok
+  end
+
+  @impl true
+  def before_execution(_opts) do
+    IO.inspect("Before execution")
+    :ok
+  end
+
+  @impl true
+  def after_execution(_opts) do
+    IO.inspect("After execution")
+    :ok
+  end
+end
diff --git a/test/support/router/plug.ex b/test/support/router/plug.ex
index 8ee4543b..af434244 100644
--- a/test/support/router/plug.ex
+++ b/test/support/router/plug.ex
@@ -25,7 +25,12 @@ defmodule Inngest.Test.PlugRouter do
     |> send_resp(200, data)
   end
 
-  inngest("/api/inngest", path: "test/support/cases/*")
+  inngest("/api/inngest",
+    functions: "test/support/cases/*",
+    middleware: [
+      Inngest.Test.Case.Middleware.Test
+    ]
+  )
 
   match _ do
     send_resp(conn, 404, "oops\n")