diff --git a/.gitignore b/.gitignore
index 9607671..232de76 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,5 @@
 /deps
 erl_crash.dump
 *.ez
+
+/doc
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..7ec269d
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2015 Gary Fleshman
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
\ No newline at end of file
diff --git a/README.md b/README.md
index 86abe60..4363532 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,65 @@
-JsonWebToken
-============
+# JSON Web Token
 
-** TODO: Add description **
+## A JSON Web Token implementation for Elixir
+
+### Description
+An Elixir implementation of the JSON Web Token (JWT) Standards Track [RFC 7519][rfc7519]
+
+### Philosophy & design goals
+* Minimal API surface area
+* Clear separation and conformance to underlying standards
+  - JSON Web Signature (JWS) Standards Track [RFC 7515][rfc7515]
+  - JSON Web Algorithms (JWA) Standards Track [RFC 7518][rfc7518]
+* Thorough test coverage
+* Modularity for comprehension and extensibility
+* Fail fast and hard, with maximally strict validation
+  - Inspired by [The Harmful Consequences of Postel's Maxim][thomson-postel]
+* Implement only the REQUIRED elements of the JWT standard (initially)
+
+## Usage
+
+### JsonWebToken.sign(claims, options)
+
+Returns a JSON Web Token string
+
+`claims` (required) map
+
+`options` (required) map
+
+* **alg** (optional, default: `HS256`)
+* **key** (required unless alg is 'none')
+
+### JsonWebToken.verify(jwt, options)
+
+Returns either:
+* a JWT claims set map, if the Message Authentication Code (MAC), or signature, is verified
+* a string, 'Invalid', otherwise
+
+`jwt` (required) is a JSON web token string
+
+`options` (required) map
+
+* **alg** (optional, default: `HS256`)
+* **key** (required unless alg is 'none')
+
+### Supported encryption algorithms
+The 2 REQUIRED JWT algorithms
+
+- HMAC using SHA-256 per [RFC 2104][rfc2104]
+- none (unsecured)
+
+### Supported Elixir versions
+Elixir 1.0.5 and up
+
+### Limitations
+Future implementation may include these features:
+
+- Representation of a JWT as a JSON Web Encryption (JWE) [RFC 7516][rfc7516]
+- RECOMMENDED or OPTIONAL encryption algorithms
+- OPTIONAL nested JWTs
+
+[rfc2104]: http://tools.ietf.org/html/rfc2104
+[rfc7515]: http://tools.ietf.org/html/rfc7515
+[rfc7516]: http://tools.ietf.org/html/rfc7516
+[rfc7518]: http://tools.ietf.org/html/rfc7518
+[rfc7519]: http://tools.ietf.org/html/rfc7519
diff --git a/lib/json_web_token/format/base_64_url.ex b/lib/json_web_token/format/base_64_url.ex
new file mode 100644
index 0000000..6056f27
--- /dev/null
+++ b/lib/json_web_token/format/base_64_url.ex
@@ -0,0 +1,49 @@
+defmodule JsonWebToken.Format.Base64Url do
+  @moduledoc """
+  Provide base64url encoding and decoding functions without padding, based upon standard base64 encoding
+  and decoding functions that do use padding
+
+  see http://tools.ietf.org/html/rfc7515#appendix-C
+  """
+
+  @doc """
+  Given a string, return a url_encode64 string with all trailing "=" padding removed
+
+  ## Example
+      iex> JsonWebToken.Format.Base64Url.encode("foo")
+      "Zm9v"
+  """
+  def encode(string) do
+    string
+    |> Base.url_encode64
+    |> base64_padding_removed
+  end
+
+  defp base64_padding_removed(encoded), do: String.rstrip(encoded, ?=)
+
+  @doc """
+  Given a string encoded as url_encode64, add trailing "=" padding and return a decoded string
+
+  ## Example
+      iex> JsonWebToken.Format.Base64Url.decode("YmFy")
+      "bar"
+
+  The number of "=" padding characters that need to be added to the end of a url_encode64-encoded
+  string without padding to turn it into one with padding is a deterministic function of the length
+  of the encoded string.
+  """
+  def decode(string) do
+    string
+    |> base64_padding_added
+    |> Base.url_decode64!
+  end
+
+  defp base64_padding_added(str) do
+    mod = rem(String.length(str), 4)
+    str <> padding(mod)
+  end
+
+  defp padding(0), do: ""
+  defp padding(1), do: raise "Invalid base64 string"
+  defp padding(mod), do: String.duplicate("=", (4 - mod))
+end
diff --git a/mix.exs b/mix.exs
index a60dbe7..e60c9be 100644
--- a/mix.exs
+++ b/mix.exs
@@ -2,19 +2,26 @@ defmodule JsonWebToken.Mixfile do
   use Mix.Project
 
   def project do
-    [app: :json_web_token,
-     version: "0.0.1",
-     elixir: "~> 1.0",
-     build_embedded: Mix.env == :prod,
-     start_permanent: Mix.env == :prod,
-     deps: deps]
+    [
+      app: :json_web_token,
+      version: "0.0.1",
+      elixir: "~> 1.0",
+      build_embedded: Mix.env == :prod,
+      start_permanent: Mix.env == :prod,
+      deps: deps,
+      test_coverage: [tool: ExCoveralls]
+    ]
   end
 
   # Configuration for the OTP application
   #
   # Type `mix help compile.app` for more information
   def application do
-    [applications: [:logger]]
+    [
+      applications: [
+        :logger
+      ]
+    ]
   end
 
   # Dependencies can be Hex packages:
@@ -27,6 +34,10 @@ defmodule JsonWebToken.Mixfile do
   #
   # Type `mix help deps` for more examples and options
   defp deps do
-    []
+    [
+      {:earmark, "~> 0.1", only: :dev},
+      {:ex_doc, "~> 0.7", only: :dev},
+      {:excoveralls, "~> 0.3", only: :test}
+    ]
   end
 end
diff --git a/mix.lock b/mix.lock
new file mode 100644
index 0000000..a9ddd43
--- /dev/null
+++ b/mix.lock
@@ -0,0 +1,8 @@
+%{"earmark": {:hex, :earmark, "0.1.17"},
+  "ex_doc": {:hex, :ex_doc, "0.7.3"},
+  "excoveralls": {:hex, :excoveralls, "0.3.11"},
+  "exjsx": {:hex, :exjsx, "3.2.0"},
+  "hackney": {:hex, :hackney, "1.2.0"},
+  "idna": {:hex, :idna, "1.0.2"},
+  "jsx": {:hex, :jsx, "2.6.2"},
+  "ssl_verify_hostname": {:hex, :ssl_verify_hostname, "1.0.5"}}
diff --git a/test/json_web_token/format/base64_url_test.exs b/test/json_web_token/format/base64_url_test.exs
new file mode 100644
index 0000000..b69b46b
--- /dev/null
+++ b/test/json_web_token/format/base64_url_test.exs
@@ -0,0 +1,66 @@
+defmodule JsonWebToken.Format.Base64UrlTest do
+  use ExUnit.Case
+
+  alias JsonWebToken.Format.Base64Url
+
+  doctest Base64Url
+
+  defp decode_encoded_matches?(str) do
+    encoded = Base64Url.encode(str)
+    str == Base64Url.decode(encoded)
+  end
+
+  test "decode/1 encode/1 typical" do
+    assert decode_encoded_matches?("{\"typ\":\"JWT\", \"alg\":\"HS256\"}")
+  end
+
+  test "decode/1 encode/1 w whitespace" do
+    assert decode_encoded_matches?("{\"typ\":\"JWT\" ,  \"alg\":\"HS256\"  }")
+  end
+
+  test "decode/1 encode/1 w line feed and carriage return" do
+    assert decode_encoded_matches?("{\"typ\":\"JWT\",/n \"a/rlg\":\"HS256\"}")
+  end
+
+  defp given_encoded_matches?(str, encoded) do
+    Base64Url.encode(str) == encoded &&
+      Base64Url.decode(encoded) == str
+  end
+
+  test "decode/1 w no padding char" do
+    str = "{\"typ\":\"JWT\", \"alg\":\"none\"}"
+    encoded = "eyJ0eXAiOiJKV1QiLCAiYWxnIjoibm9uZSJ9"
+    assert given_encoded_matches?(str, encoded)
+  end
+
+  test "decode/1 w 1 padding char present" do
+    str = "{\"typ\":\"JWT\", \"alg\":\"algorithm\"}"
+    encoded = "eyJ0eXAiOiJKV1QiLCAiYWxnIjoiYWxnb3JpdGhtIn0="
+    assert Base64Url.decode(encoded) == str
+  end
+
+  test "decode/1 w 1 padding char removed" do
+    str = "{\"typ\":\"JWT\", \"alg\":\"algorithm\"}"
+    encoded = "eyJ0eXAiOiJKV1QiLCAiYWxnIjoiYWxnb3JpdGhtIn0"
+    assert given_encoded_matches?(str, encoded)
+  end
+
+  test "decode/1 w 2 padding char present" do
+    str = "{\"typ\":\"JWT\", \"alg\":\"HS256\"}"
+    encoded = "eyJ0eXAiOiJKV1QiLCAiYWxnIjoiSFMyNTYifQ=="
+    assert Base64Url.decode(encoded) == str
+  end
+
+  test "decode/1 w 2 padding char removed" do
+    str = "{\"typ\":\"JWT\", \"alg\":\"HS256\"}"
+    encoded = "eyJ0eXAiOiJKV1QiLCAiYWxnIjoiSFMyNTYifQ"
+    assert given_encoded_matches?(str, encoded)
+  end
+
+  test "decode/1 w invalid encoding" do
+    message = "Invalid base64 string"
+    assert_raise RuntimeError, message, fn ->
+      Base64Url.decode("InR5cCI6IkpXVCIsICJhbGciOiJub25lI")
+    end
+  end
+end