diff --git a/lib/ciphers/rot13.ex b/lib/ciphers/rot13.ex
new file mode 100644
index 0000000..48fe1bd
--- /dev/null
+++ b/lib/ciphers/rot13.ex
@@ -0,0 +1,36 @@
+defmodule Algorithms.Ciphers.Rot13 do
+  @moduledoc """
+    subtition cipher for alphabets by rotating about the alphabet list  13 places (https://en.wikipedia.org/wiki/ROT13)
+
+    ## Parameters
+
+    - text: Input number to insert the a new bit.
+
+    ## Examples
+
+        iex> Rot13.encode("hello")
+        14
+  """
+
+  def encode(string)
+
+  def encode(<<char>> <> tail) do
+    <<rotate(char)>> <> encode(tail)
+  end
+
+  def encode(_), do: ""
+
+  def rotate(char) when char >= ?a and char <= ?z do
+    ?a + rem(char - ?a + 13, 26)
+  end
+
+  def rotate(char) when char >= ?A and char <= ?Z do
+    ?A + rem(char - ?A + 13, 26)
+  end
+
+  def rotate(char), do: char
+
+  def decode(string) do
+    encode(string)
+  end
+end
diff --git a/test/ciphers/rot13.exs b/test/ciphers/rot13.exs
new file mode 100644
index 0000000..f82f362
--- /dev/null
+++ b/test/ciphers/rot13.exs
@@ -0,0 +1,34 @@
+defmodule Algorithms.Ciphers.Rot13Test do
+  alias Algorithms.Ciphers.Rot13
+
+  use ExUnit.Case
+
+  test "encode and decode" do
+    assert Rot13.encode("Hello, World!") == "Uryyb, Jbeyq!"
+    assert Rot13.decode("Uryyb, Jbeyq!") == "Hello, World!"
+  end
+
+  test "encode and decode with uppercase letters" do
+    assert Rot13.encode("HELLO, WORLD!") == "URYYB, JBEYQ!"
+    assert Rot13.decode("URYYB, JBEYQ!") == "HELLO, WORLD!"
+  end
+
+  test "encode and decode with special characters" do
+    assert Rot13.encode("Hello, World! @#$%^&*()") == "Uryyb, Jbeyq! @#$%^&*()"
+    assert Rot13.decode("Uryyb, Jbeyq! @#$%^&*()") == "Hello, World! @#$%^&*()"
+  end
+
+  describe "Rot13.encode/1" do
+    test "encodes a string" do
+      assert Rot13.encode("Hello, World!") == "Uryyb, Jbeyq!"
+    end
+
+    test "encodes a string with uppercase letters" do
+      assert Rot13.encode("HELLO, WORLD!") == "URYYB, JBEYQ!"
+    end
+
+    test "encodes a string with special characters" do
+      assert Rot13.encode("Hello, World! @#$%^&*()") == "Uryyb, Jbeyq! @#$%^&*()"
+    end
+  end
+end