diff --git a/lib/koans/19_genservers.ex b/lib/koans/19_genservers.ex
new file mode 100644
index 0000000..537e72d
--- /dev/null
+++ b/lib/koans/19_genservers.ex
@@ -0,0 +1,141 @@
+defmodule GenServers do
+  use Koans
+
+  @intro "GenServers"
+
+  defmodule BicycleLock do
+    use GenServer
+
+    @init_password 1234
+
+    #####
+    # External API
+
+    def start_link(init_password \\ @init_password) do
+      # The __MODULE__ macro returns the current module name as an atom
+      GenServer.start_link(__MODULE__, init_password, name: __MODULE__)
+    end
+
+    def unlock(password) do
+      GenServer.call(__MODULE__, {:unlock, password})
+    end
+
+    def password_reset(old_password, new_password) do
+      GenServer.cast(__MODULE__, {:reset, old_password, new_password})
+    end
+
+    def owner_info do
+      GenServer.call(__MODULE__, :get_owner_info)
+    end
+
+    ####
+    # GenServer implementation
+
+    def init(args) do
+     {:ok, args && args || @init_password} 
+    end
+    
+    def handle_call(:get_password, _from, current_password) do
+     {:reply, current_password, current_password} 
+    end
+
+    def handle_call(:get_bike_brand, _from, current_state) do
+      {:reply, "Tribe Bicycle Co.", current_state}
+    end
+
+    def handle_call(:get_bike_name, _from, current_state) do
+      {:reply, "CRMO Series", current_state}
+    end
+
+    def handle_call(:get_owner_info, _from, current_state) do
+      {:reply, {:ok, "Argh...Jack Sparrow's password is: #{current_state}"}, current_state}
+    end
+
+    def handle_call(:get_multi, _from, current_state) do
+      {:reply, {:ok, ["this", "is", "sparta"]}, current_state}
+    end
+
+    def handle_call(:name_check, _from, current_state) do
+      {:reply, "Congrats! Your process was successfully named.", current_state}
+    end
+    
+    def handle_call({:unlock, password}, _from, current_password) do
+      case password do
+        password when password === current_password ->
+          {:reply, {:ok, "Bicycle unlocked!"}, current_password}
+        _ -> 
+          {:reply, {:error, "Incorrect password!"}, current_password}
+      end
+    end
+    
+    def handle_cast({:reset, old_password, new_password}, current_password) do
+      case old_password do
+        old_password when old_password == current_password ->
+          {:noreply, new_password}
+        _ ->
+          {:noreply, current_password} 
+      end
+    end
+  end
+
+  koan "Servers that are created and initialized successfully returns a tuple that holds the PID of the server" do
+    {:ok, pid} = GenServer.start_link(BicycleLock, nil)
+    assert is_pid(pid) == ___
+  end
+
+  koan "When starting a GenServer you can set it's initial state" do
+    {:ok, pid} = GenServer.start_link(BicycleLock, "Hey Arnold!")
+    assert GenServer.call(pid, :get_password) == ___
+  end
+
+  koan "The handle_call callback is synchronous so it will block until a reply is received" do
+    {:ok, pid} = GenServer.start_link(BicycleLock, nil)
+    assert GenServer.call(pid, :get_password) == ___
+  end
+
+  koan "A server can support multiple actions by implementing multiple handle_call functions" do
+    {:ok, pid} = GenServer.start_link(BicycleLock, nil)
+    assert GenServer.call(pid, :get_bike_brand) == ___
+    assert GenServer.call(pid, :get_bike_name) == ___
+  end
+
+  koan "A handler can return multiple values" do
+    {:ok, pid} = GenServer.start_link(BicycleLock, nil)
+    {:ok, multi_values} = GenServer.call(pid, :get_multi)
+    assert multi_values == ___
+  end
+
+  koan "The handle_cast callback handles asynchronous messages" do
+    {:ok, pid} = GenServer.start_link(BicycleLock, nil)
+    GenServer.cast(pid, {:reset, 1234, "Hello"})
+    assert GenServer.call(pid, :get_password) == ___
+  end
+
+  koan "Handlers can also return error responses" do
+    {:ok, pid} = GenServer.start_link(BicycleLock, nil)
+    assert GenServer.call(pid, {:unlock, 2017}) == ___
+  end
+
+  koan "Referencing processes by their PID gets old pretty quickly, so let's name them" do
+    {:ok, pid} = GenServer.start_link(BicycleLock, nil, name: :bike_lock)
+    assert GenServer.call(:bike_lock, :name_check) == ___
+  end
+
+  koan "Our server works but it's pretty ugly to use; so lets use a cleaner interface" do
+    BicycleLock.start_link
+    assert BicycleLock.unlock(1234) == ___
+  end
+
+  koan "Let's use the remaining functions in the external API" do
+    BicycleLock.start_link(31337)
+    {_, response} = BicycleLock.unlock(31337)
+    assert response == ___
+
+    BicycleLock.password_reset(31337, "Elixir")
+    {_, response} = BicycleLock.unlock(31337)
+    assert response == ___
+
+    {_, response} = BicycleLock.owner_info 
+    assert response == ___
+  end
+end
\ No newline at end of file
diff --git a/lib/runner.ex b/lib/runner.ex
index be1d0ae..5f1d98b 100644
--- a/lib/runner.ex
+++ b/lib/runner.ex
@@ -18,6 +18,7 @@ defmodule Runner do
     Tasks,
     Agents,
     Protocols,
+    GenServers,
   ]
 
   def koan?(koan), do: Enum.member?(@modules, koan)
diff --git a/test/koans/genservers_koans_test.exs b/test/koans/genservers_koans_test.exs
new file mode 100644
index 0000000..7175ea6
--- /dev/null
+++ b/test/koans/genservers_koans_test.exs
@@ -0,0 +1,21 @@
+defmodule GenServersTests do
+  use ExUnit.Case
+  import TestHarness
+
+  test "GenServers" do
+    answers = [
+      true,
+      "Hey Arnold!",
+      1234,
+      {:multiple, ["Tribe Bicycle Co.", "CRMO Series"]},
+      ["this", "is", "sparta"],
+      "Hello",
+      {:error, "Incorrect password!"},
+      "Congrats! Your process was successfully named.",
+      {:ok, "Bicycle unlocked!"},
+      {:multiple, ["Bicycle unlocked!", "Incorrect password!", "Argh...Jack Sparrow's password is: Elixir"]},
+    ]
+
+    test_all(GenServers, answers)
+  end
+end