diff --git a/lib/zombie_survivor.ex b/lib/zombie_survivor.ex
index 34a4819..e89d1f0 100644
--- a/lib/zombie_survivor.ex
+++ b/lib/zombie_survivor.ex
@@ -2,4 +2,16 @@ defmodule ZombieSurvivor do
   @moduledoc """
   Documentation for ZombieSurvivor.
   """
+
+  @type level :: :blue | :yellow | :orange | :red
+
+  @spec level(non_neg_integer) :: level
+  def level(experience) do
+    case experience do
+      x when x > 42 -> :red
+      x when x > 18 -> :orange
+      x when x > 6 -> :yellow
+      _ -> :blue
+    end
+  end
 end
diff --git a/lib/zombie_survivor/game.ex b/lib/zombie_survivor/game.ex
index 76c004e..a4e5eba 100644
--- a/lib/zombie_survivor/game.ex
+++ b/lib/zombie_survivor/game.ex
@@ -27,4 +27,11 @@ defmodule ZombieSurvivor.Game do
       Survivor.dead?(survivor)
     end)
   end
+
+  @spec level(Game.t()) :: ZombieSurvivor.level()
+  def level(game) do
+    game.survivors
+    |> Enum.reduce(0, fn {_, s}, acc -> max(s.experience, acc) end)
+    |> ZombieSurvivor.level()
+  end
 end
diff --git a/lib/zombie_survivor/survivor.ex b/lib/zombie_survivor/survivor.ex
index 999274c..7968f26 100644
--- a/lib/zombie_survivor/survivor.ex
+++ b/lib/zombie_survivor/survivor.ex
@@ -4,10 +4,11 @@ defmodule ZombieSurvivor.Survivor do
   @type t :: %__MODULE__{
           name: String.t(),
           wounds: non_neg_integer,
-          equipment: [String.t()]
+          equipment: [String.t()],
+          experience: non_neg_integer
         }
 
-  defstruct name: "", wounds: 0, equipment: []
+  defstruct name: "", wounds: 0, equipment: [], experience: 0
 
   @spec new([{atom, any}]) :: Survivor.t()
   def new(opts \\ []), do: struct(__MODULE__, opts)
@@ -15,6 +16,9 @@ defmodule ZombieSurvivor.Survivor do
   @spec dead?(Survivor.t()) :: boolean
   def dead?(survivor), do: survivor.wounds >= 2
 
+  @spec level(Survivor.t()) :: ZombieSurvivor.level()
+  def level(survivor), do: ZombieSurvivor.level(survivor.experience)
+
   @spec max_actions(Survivor.t()) :: non_neg_integer
   def max_actions(_survivor) do
     3
@@ -26,6 +30,11 @@ defmodule ZombieSurvivor.Survivor do
     |> discard_equipment()
   end
 
+  @spec kill_zombies(Survivor.t(), non_neg_integer) :: Survivor.t()
+  def kill_zombies(survivor, count \\ 1) do
+    %{survivor | experience: survivor.experience + count}
+  end
+
   @spec max_equipment(Survivor.t()) :: non_neg_integer
   def max_equipment(%Survivor{} = survivor) do
     5 - survivor.wounds
diff --git a/test/game_test.exs b/test/game_test.exs
index 63aac40..f54d03d 100644
--- a/test/game_test.exs
+++ b/test/game_test.exs
@@ -11,6 +11,10 @@ defmodule GameTest do
     test "that has 0 survivors" do
       assert Map.size(Game.new().survivors) == 0
     end
+
+    test "that's at level blue" do
+      assert Game.level(Game.new()) == :blue
+    end
   end
 
   describe "add_survivor/1" do
@@ -69,4 +73,32 @@ defmodule GameTest do
       refute Game.ended?(g)
     end
   end
+
+  describe "level/1" do
+    test "returns the level of the highest levelled survivor" do
+      g =
+        Game.new()
+        |> Game.add_survivor(@new_survivor)
+
+      assert Game.level(g) == :blue
+
+      g =
+        g
+        |> Game.add_survivor(Survivor.new(name: "Eric", experience: 10))
+
+      assert Game.level(g) == :yellow
+
+      g =
+        g
+        |> Game.add_survivor(Survivor.new(name: "Jack", experience: 20))
+
+      assert Game.level(g) == :orange
+
+      g =
+        g
+        |> Game.add_survivor(Survivor.new(name: "Liru", experience: 1_000_000))
+
+      assert Game.level(g) == :red
+    end
+  end
 end
diff --git a/test/survivor_test.exs b/test/survivor_test.exs
index 4bf445c..e1f9d1e 100644
--- a/test/survivor_test.exs
+++ b/test/survivor_test.exs
@@ -14,6 +14,14 @@ defmodule SurvivorTest do
     test "gives a survivor with 0 wounds" do
       assert %Survivor{wounds: 0} = Survivor.new()
     end
+
+    test "gives a survivor with 0 experience" do
+      assert %Survivor{experience: 0} = Survivor.new()
+    end
+
+    test "gives a survivor at level blue" do
+      assert Survivor.level(Survivor.new()) == :blue
+    end
   end
 
   describe "dead?/1" do
@@ -35,6 +43,38 @@ defmodule SurvivorTest do
     end
   end
 
+  describe "kill_zombies/1" do
+    # TODO: Property testing, always increments
+    test "increases experience by 1" do
+      s =
+        Survivor.new()
+        |> Survivor.kill_zombies()
+
+      assert s.experience == 1
+    end
+  end
+
+  describe "level/1" do
+    [
+      {:blue, :yellow, 6},
+      {:yellow, :orange, 18},
+      {:orange, :red, 42}
+    ]
+    |> Enum.each(fn {old, new, threshold} ->
+      @old old
+      @new new
+      @threshold threshold
+      test "upgrades from #{@old} to #{@new} when exceeding #{@threshold} experience" do
+        s = Survivor.new(experience: @threshold)
+        assert Survivor.level(s) == @old
+
+        s = s |> Survivor.kill_zombies()
+
+        assert Survivor.level(s) == @new
+      end
+    end)
+  end
+
   describe "max_actions/1" do
     test "returns 3 for a new survivor" do
       s = Survivor.new()