diff --git a/README.md b/README.md
index ac964f2..5eed06f 100644
--- a/README.md
+++ b/README.md
@@ -15,6 +15,36 @@ def deps do
 end
 ```
 
-Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc)
-and published on [HexDocs](https://hexdocs.pm). Once published, the docs can
-be found at [https://hexdocs.pm/base62_uuid_field](https://hexdocs.pm/base62_uuid_field).
+## Usage
+
+This Ecto type builds on top of the existing `Ecto.UUID` type, except that it ensures that the types at runtime are represented as [Base62-encoded UUIDs](https://github.com/jclem/base62_uuid).
+
+For example, given an `identity_users` table with a `:binary_id` primary key:
+
+```elixir
+create table(:identity_users, primary_key: false) do
+  add :id, :binary_id, primary_key: true
+end
+```
+
+We can have Base62-encoded primary keys at runtime instead of much longer and less URL-friendly hexadecimal-encoded UUIDs.
+
+```elixir
+defmodule App.Identity.User do
+  use Ecto.Schema
+
+  @primary_key {:id, Base62UUIDField, autogenerate: true}
+
+  # ...etc.
+end
+```
+
+```elixir
+iex> %App.Identity.User{} |> App.Identity.User.changeset(%{}) |> App.Repo.insert!()
+%App.Identity.User{
+  __meta__: #Ecto.Schema.Metadata<:loaded, "identity_users">,
+  id: "6UupZ56JriyqxwjYXR9Aiz",
+  inserted_at: ~N[2018-12-13 18:22:57],
+  updated_at: ~N[2018-12-13 18:22:57]
+}
+```
diff --git a/lib/base62_uuid_field.ex b/lib/base62_uuid_field.ex
index 8fbcbc3..c2da823 100644
--- a/lib/base62_uuid_field.ex
+++ b/lib/base62_uuid_field.ex
@@ -1,18 +1,40 @@
 defmodule Base62UUIDField do
   @moduledoc """
-  Documentation for Base62UUIDField.
+  A field that is stored as a v4 UUID but presented as a Base62-encoded binary string.
   """
 
-  @doc """
-  Hello world.
+  @behaviour Ecto.Type
 
-  ## Examples
+  @spec type() :: :string
+  def type, do: :string
 
-      iex> Base62UUIDField.hello()
-      :world
+  @spec cast(any) :: {:ok, String.t()} | :error
+  def cast(val) when is_binary(val), do: {:ok, val}
+  def cast(_), do: :error
 
-  """
-  def hello do
-    :world
+  @spec dump(any) :: {:ok, any} | :error
+  def dump(val) when is_binary(val) do
+    with {:ok, decoded} <- Base62UUID.decode(val) do
+      Ecto.UUID.dump(decoded)
+    else
+      _ -> :error
+    end
+  end
+
+  def dump(_), do: :error
+
+  @spec load(any) :: {:ok, any} | :error
+  def load(val) when is_binary(val) do
+    with {:ok, loaded} <- Ecto.UUID.load(val),
+         {:ok, decoded} <- Base62UUID.encode(loaded) do
+      {:ok, decoded}
+    else
+      _ -> :error
+    end
   end
+
+  def load(_), do: :error
+
+  @spec autogenerate() :: String.t()
+  def autogenerate, do: Base62UUID.generate()
 end
diff --git a/mix.exs b/mix.exs
index ce11bb5..b711fda 100644
--- a/mix.exs
+++ b/mix.exs
@@ -39,6 +39,7 @@ defmodule Base62UUIDField.MixProject do
   defp deps do
     [
       {:base62_uuid, "~> 2.0.0"},
+      {:ecto, "~> 3.0.5"},
       {:ex_doc, "~> 0.19.1", only: [:dev]},
       {:excoveralls, "~> 0.10.3", only: [:test]}
     ]
diff --git a/mix.lock b/mix.lock
index ead21fe..25633ab 100644
--- a/mix.lock
+++ b/mix.lock
@@ -3,7 +3,9 @@
   "base62_uuid": {:hex, :base62_uuid, "2.0.0", "6901f9692aa8791e95f0305309628056bf79c9fcc2949cbe78c43ae7c19d3990", [:mix], [{:base62, "~> 1.2.0", [hex: :base62, repo: "hexpm", optional: false]}, {:uuid, "~> 1.1.5", [hex: :uuid, repo: "hexpm", optional: false]}], "hexpm"},
   "certifi": {:hex, :certifi, "2.4.2", "75424ff0f3baaccfd34b1214184b6ef616d89e420b258bb0a5ea7d7bc628f7f0", [:rebar3], [{:parse_trans, "~>3.3", [hex: :parse_trans, repo: "hexpm", optional: false]}], "hexpm"},
   "custom_base": {:hex, :custom_base, "0.2.1", "4a832a42ea0552299d81652aa0b1f775d462175293e99dfbe4d7dbaab785a706", [:mix], [], "hexpm"},
+  "decimal": {:hex, :decimal, "1.6.0", "bfd84d90ff966e1f5d4370bdd3943432d8f65f07d3bab48001aebd7030590dcc", [:mix], [], "hexpm"},
   "earmark": {:hex, :earmark, "1.3.0", "17f0c38eaafb4800f746b457313af4b2442a8c2405b49c645768680f900be603", [:mix], [], "hexpm"},
+  "ecto": {:hex, :ecto, "3.0.5", "bf9329b56f781a67fdb19e92e6d9ed79c5c8b31d41653b79dafb7ceddfbe87e0", [:mix], [{:decimal, "~> 1.6", [hex: :decimal, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: true]}, {:poison, "~> 2.2 or ~> 3.0", [hex: :poison, repo: "hexpm", optional: true]}], "hexpm"},
   "ex_doc": {:hex, :ex_doc, "0.19.1", "519bb9c19526ca51d326c060cb1778d4a9056b190086a8c6c115828eaccea6cf", [:mix], [{:earmark, "~> 1.1", [hex: :earmark, repo: "hexpm", optional: false]}, {:makeup_elixir, "~> 0.7", [hex: :makeup_elixir, repo: "hexpm", optional: false]}], "hexpm"},
   "excoveralls": {:hex, :excoveralls, "0.10.3", "b090a3fbcb3cfa136f0427d038c92a9051f840953ec11b40ee74d9d4eac04d1e", [:mix], [{:hackney, "~> 1.13", [hex: :hackney, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm"},
   "hackney": {:hex, :hackney, "1.14.3", "b5f6f5dcc4f1fba340762738759209e21914516df6be440d85772542d4a5e412", [:rebar3], [{:certifi, "2.4.2", [hex: :certifi, repo: "hexpm", optional: false]}, {:idna, "6.0.0", [hex: :idna, repo: "hexpm", optional: false]}, {:metrics, "1.0.1", [hex: :metrics, repo: "hexpm", optional: false]}, {:mimerl, "1.0.2", [hex: :mimerl, repo: "hexpm", optional: false]}, {:ssl_verify_fun, "1.1.4", [hex: :ssl_verify_fun, repo: "hexpm", optional: false]}], "hexpm"},
diff --git a/test/base62_uuid_field_test.exs b/test/base62_uuid_field_test.exs
index 48d8e49..dd3ef5f 100644
--- a/test/base62_uuid_field_test.exs
+++ b/test/base62_uuid_field_test.exs
@@ -1,8 +1,55 @@
 defmodule Base62UUIDFieldTest do
-  use ExUnit.Case
-  doctest Base62UUIDField
+  use ExUnit.Case, async: true
 
-  test "greets the world" do
-    assert Base62UUIDField.hello() == :world
+  setup do
+    uuid = Ecto.UUID.generate()
+    {:ok, ecto_dumped_uuid} = Ecto.UUID.dump(uuid)
+    {:ok, uuid: uuid, encoded_uuid: Base62UUID.encode!(uuid), ecto_dumped_uuid: ecto_dumped_uuid}
+  end
+
+  test ".autogenerate generates a Base62 UUID" do
+    assert String.length(Base62UUIDField.autogenerate()) == 22
+  end
+
+  test ".type is a string" do
+    assert Base62UUIDField.type() == :string
+  end
+
+  test ".cast casts to a string" do
+    assert Base62UUIDField.cast("1") == {:ok, "1"}
+  end
+
+  test ".cast on a non-binary returns an error" do
+    assert Base62UUIDField.cast(1) == :error
+  end
+
+  test ".dump decodes the value to a UUID", %{
+    encoded_uuid: encoded_uuid,
+    ecto_dumped_uuid: ecto_dumped_uuid
+  } do
+    assert Base62UUIDField.dump(encoded_uuid) == {:ok, ecto_dumped_uuid}
+  end
+
+  test ".dump on a non-binary returns an error" do
+    assert Base62UUIDField.dump(1) == :error
+  end
+
+  test ".dump returns an error for a non-UUID" do
+    assert Base62UUIDField.dump("!") == :error
+  end
+
+  test ".load encodes the value to a Base62 UUID", %{
+    ecto_dumped_uuid: ecto_dumped_uuid,
+    encoded_uuid: encoded_uuid
+  } do
+    assert Base62UUIDField.load(ecto_dumped_uuid) == {:ok, encoded_uuid}
+  end
+
+  test ".load on a non-binary returns an error" do
+    assert Base62UUIDField.load(1) == :error
+  end
+
+  test ".load returns an error for a non-UUID" do
+    assert Base62UUIDField.load("not-a-uuid") == :error
   end
 end