diff --git a/lib/koans/18_genservers.ex b/lib/koans/18_genservers.ex
new file mode 100644
index 0000000..8ad4589
--- /dev/null
+++ b/lib/koans/18_genservers.ex
@@ -0,0 +1,153 @@
+defmodule GenServers do
+  use Koans
+
+  @intro "GenServers"
+
+  defmodule Laptop do
+    use GenServer
+
+    #####
+    # External API
+
+    def start_link(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 owner_name do
+      GenServer.call(__MODULE__, :get_owner_name)
+    end
+
+    def manufacturer do
+      GenServer.call(__MODULE__, :get_manufacturer)
+    end
+
+    def laptop_type do
+      GenServer.call(__MODULE__, :get_type)
+    end
+
+    def retrieve_password do
+      GenServer.call(__MODULE__, :get_password)
+    end
+
+    def laptop_specs do
+      GenServer.call(__MODULE__, :get_specs)
+    end
+
+    def change_password(old_password, new_password) do
+      GenServer.cast(__MODULE__, {:change_password, old_password, new_password})
+    end
+
+    ####
+    # GenServer implementation
+    
+    def handle_call(:get_password, _from, current_password) do
+     {:reply, current_password, current_password} 
+    end
+
+    def handle_call(:get_manufacturer, _from, current_state) do
+      {:reply, "Apple Inc.", current_state}
+    end
+
+    def handle_call(:get_type, _from, current_state) do
+      {:reply, "MacBook Pro", current_state}
+    end
+
+    def handle_call(:get_owner_name, _from, current_state) do
+      {:reply, {:ok, "Jack Sparrow"}, current_state}
+    end
+
+    def handle_call(:get_specs, _from, current_state) do
+      {:reply, {:ok, ["2.9 GHz Intel Core i5"], 8192, :intel_iris_graphics}, 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, "Laptop unlocked!"}, current_password}
+        _ -> 
+          {:reply, {:error, "Incorrect password!"}, current_password}
+      end
+    end
+    
+    def handle_cast({:change_password, 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(Laptop, "3kr3t!")
+    assert is_pid(pid) == ___
+  end
+
+  koan "When starting a GenServer you can set it's initial state" do
+    {:ok, pid} = GenServer.start_link(Laptop, "3kr3t!")
+    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(Laptop, "3kr3t!")
+    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(Laptop, "3kr3t!")
+    assert GenServer.call(pid, :get_manufacturer) == ___
+    assert GenServer.call(pid, :get_type) == ___
+  end
+
+  koan "A handler can return multiple values and of different types" do
+    {:ok, pid} = GenServer.start_link(Laptop, "3kr3t!")
+    {:ok, processor, memory, graphics} = GenServer.call(pid, :get_specs)
+    assert processor == ___
+    assert memory == ___
+    assert graphics == ___
+  end
+
+  koan "The handle_cast callback handles asynchronous messages" do
+    {:ok, pid} = GenServer.start_link(Laptop, "3kr3t!")
+    GenServer.cast(pid, {:change_password, "3kr3t!", "73x7!n9"})
+    assert GenServer.call(pid, :get_password) == ___
+  end
+
+  koan "Handlers can also return error responses" do
+    {:ok, pid} = GenServer.start_link(Laptop, "3kr3t!")
+    assert GenServer.call(pid, {:unlock, "81u3pr!n7"}) == ___
+  end
+
+  koan "Referencing processes by their PID gets old pretty quickly, so let's name them" do
+    {:ok, _} = GenServer.start_link(Laptop, "3kr3t!", name: :macbook)
+    assert GenServer.call(:macbook, :name_check) == ___
+  end
+
+  koan "Our server works but it's pretty ugly to use; so lets use a cleaner interface" do
+    Laptop.start_link("EL!73")
+    assert Laptop.unlock("EL!73") == ___
+  end
+
+  koan "Let's use the remaining functions in the external API" do
+    Laptop.start_link("EL!73")
+    {_, response} = Laptop.unlock("EL!73")
+    assert response == ___
+
+    Laptop.change_password("EL!73", "Elixir")
+    {_, response} = Laptop.unlock("EL!73")
+    assert response == ___
+
+    {_, response} = Laptop.owner_name 
+    assert response == ___
+  end
+end
\ No newline at end of file
diff --git a/lib/koans/18_protocols.ex b/lib/koans/19_protocols.ex
similarity index 100%
rename from lib/koans/18_protocols.ex
rename to lib/koans/19_protocols.ex
diff --git a/lib/runner.ex b/lib/runner.ex
index be1d0ae..0c7664c 100644
--- a/lib/runner.ex
+++ b/lib/runner.ex
@@ -17,6 +17,7 @@ defmodule Runner do
     Processes,
     Tasks,
     Agents,
+    GenServers,
     Protocols,
   ]
 
diff --git a/test/koans/genservers_koans_test.exs b/test/koans/genservers_koans_test.exs
new file mode 100644
index 0000000..b8cae92
--- /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,
+      "3kr3t!",
+      "3kr3t!",
+      {:multiple, ["Apple Inc.", "MacBook Pro"]},
+      {:multiple, [["2.9 GHz Intel Core i5"], 8192, :intel_iris_graphics]},
+      "73x7!n9",
+      {:error, "Incorrect password!"},
+      "Congrats! Your process was successfully named.",
+      {:ok, "Laptop unlocked!"},
+      {:multiple, ["Laptop unlocked!", "Incorrect password!", "Jack Sparrow"]},
+    ]
+
+    test_all(GenServers, answers)
+  end
+end