diff --git a/lib/lob/check.ex b/lib/lob/check.ex
new file mode 100644
index 0000000..d46e709
--- /dev/null
+++ b/lib/lob/check.ex
@@ -0,0 +1,8 @@
+defmodule Lob.Check do
+  @moduledoc """
+  Module implementing the Lob checks API.
+  """
+
+  use Lob.ResourceBase, endpoint: "checks", methods: [:create, :retrieve, :list, :delete]
+
+end
diff --git a/lib/lob/letter.ex b/lib/lob/letter.ex
new file mode 100644
index 0000000..bc76063
--- /dev/null
+++ b/lib/lob/letter.ex
@@ -0,0 +1,8 @@
+defmodule Lob.Letter do
+  @moduledoc """
+  Module implementing the Lob letters API.
+  """
+
+  use Lob.ResourceBase, endpoint: "letters", methods: [:create, :retrieve, :list, :delete]
+
+end
diff --git a/test/assets/8.5x11.pdf b/test/assets/8.5x11.pdf
new file mode 100644
index 0000000..ea4902b
Binary files /dev/null and b/test/assets/8.5x11.pdf differ
diff --git a/test/assets/logo.png b/test/assets/logo.png
new file mode 100644
index 0000000..e7ecfe2
Binary files /dev/null and b/test/assets/logo.png differ
diff --git a/test/lob/check_test.exs b/test/lob/check_test.exs
new file mode 100644
index 0000000..d613c27
--- /dev/null
+++ b/test/lob/check_test.exs
@@ -0,0 +1,188 @@
+defmodule Lob.CheckTest do
+  use ExUnit.Case
+
+  alias Lob.Check
+
+  setup do
+    sample_address = %{
+      name: "TestAddress",
+      email: "test@test.com",
+      address_line1: "185 Berry Street",
+      address_line2: "Suite 6100",
+      address_city: "San Francisco",
+      address_state: "CA",
+      address_country: "US",
+      address_zip: "94107"
+    }
+
+    sample_check = %{
+      description: "Library Test Check #{DateTime.utc_now |> DateTime.to_string}",
+      amount: 100
+    }
+
+    # TODO(anthony): Once address API is added to wrapper, replace this ID with a created address
+    # TODO(anthony): Once bank account API is added to wrapper, replace this ID with a created bank account
+    %{
+      test_address_id: "adr_a7d78be7f746a0a7",
+      test_bank_account_id: "bank_ffbb58dbc5a51d8",
+      sample_address: sample_address,
+      sample_check: sample_check
+    }
+  end
+
+  describe "list/2" do
+
+    test "lists checks" do
+      {:ok, checks, _headers} = Check.list()
+      assert checks.object == "list"
+    end
+
+    test "includes total count" do
+      {:ok, checks, _headers} = Check.list(%{include: ["total_count"]})
+      assert Map.get(checks, :total_count) != nil
+    end
+
+    test "lists by limit" do
+      {:ok, checks, _headers} = Check.list(%{limit: 2})
+      assert checks.count == 2
+    end
+
+    test "filters by metadata" do
+      {:ok, checks, _headers} = Check.list(%{metadata: %{foo: "bar"}})
+      assert checks.count == 1
+    end
+
+  end
+
+  describe "retrieve/2" do
+
+    test "retrieves a check", %{test_address_id: test_address_id, test_bank_account_id: test_bank_account_id, sample_check: sample_check} do
+      {:ok, created_check, _headers} =
+        Check.create(%{
+          description: sample_check.description,
+          to: test_address_id,
+          from: test_address_id,
+          bank_account: test_bank_account_id,
+          amount: 42
+        })
+
+      {:ok, retrieved_check, _headers} = Check.retrieve(created_check.id)
+      assert retrieved_check.description == created_check.description
+    end
+
+  end
+
+  describe "create/2" do
+
+    test "creates a check with address_id", %{test_address_id: test_address_id, test_bank_account_id: test_bank_account_id, sample_check: sample_check} do
+      {:ok, created_check, headers} =
+        Check.create(%{
+          description: sample_check.description,
+          to: test_address_id,
+          from: test_address_id,
+          bank_account: test_bank_account_id,
+          amount: 42
+        })
+
+      assert created_check.description == sample_check.description
+      assert Enum.member?(headers, {"X-Rate-Limit-Limit", "150"})
+    end
+
+    test "creates a check with address params", %{sample_check: sample_check, test_bank_account_id: test_bank_account_id, sample_address: sample_address} do
+      {:ok, created_check, headers} =
+        Check.create(%{
+          description: sample_check.description,
+          to: sample_address,
+          from: sample_address,
+          bank_account: test_bank_account_id,
+          amount: 42
+        })
+
+      assert created_check.description == sample_check.description
+      assert Enum.member?(headers, {"X-Rate-Limit-Limit", "150"})
+    end
+
+    test "creates a check with logo, attachment and check bottom as URL", %{test_address_id: test_address_id, test_bank_account_id: test_bank_account_id, sample_check: sample_check} do
+      {:ok, created_check, headers} =
+        Check.create(%{
+          description: sample_check.description,
+          to: test_address_id,
+          from: test_address_id,
+          bank_account: test_bank_account_id,
+          amount: 42,
+          logo: "http://via.placeholder.com/100x100",
+          check_bottom: "https://s3-us-west-2.amazonaws.com/lob-assets/letter-goblue.pdf",
+          attachment: "https://s3-us-west-2.amazonaws.com/lob-assets/letter-goblue.pdf"
+        })
+
+      assert created_check.description == sample_check.description
+      assert Enum.member?(headers, {"X-Rate-Limit-Limit", "150"})
+    end
+
+    test "creates a check with logo as PNG and attachment and check bottom as PDF", %{test_address_id: test_address_id, test_bank_account_id: test_bank_account_id, sample_check: sample_check} do
+      {:ok, created_check, headers} =
+        Check.create(%{
+          description: sample_check.description,
+          to: test_address_id,
+          from: test_address_id,
+          bank_account: test_bank_account_id,
+          amount: 42,
+          logo: %{local_path: "test/assets/logo.png"},
+          check_bottom: %{local_path: "test/assets/8.5x11.pdf"},
+          attachment: %{local_path: "test/assets/8.5x11.pdf"}
+        })
+
+      assert created_check.description == sample_check.description
+      assert Enum.member?(headers, {"X-Rate-Limit-Limit", "150"})
+    end
+
+    test "creates a check with an idempotency key", %{test_address_id: test_address_id, test_bank_account_id: test_bank_account_id, sample_check: sample_check} do
+      idempotency_key = UUID.uuid4()
+
+      {:ok, created_check, _headers} =
+        Check.create(%{
+          description: sample_check.description,
+          to: test_address_id,
+          from: test_address_id,
+          bank_account: test_bank_account_id,
+          amount: 42
+        }, %{
+          "Idempotency-Key" => idempotency_key
+        })
+
+      {:ok, duplicated_postcard, _headers} =
+        Check.create(%{
+          description: "Duplicated Check",
+          to: test_address_id,
+          from: test_address_id,
+          bank_account: test_bank_account_id,
+          amount: 42
+        }, %{
+          "Idempotency-Key" => idempotency_key
+        })
+
+      assert created_check.description == duplicated_postcard.description
+    end
+
+  end
+
+  describe "delete/2" do
+
+    test "deletes a check", %{test_address_id: test_address_id, test_bank_account_id: test_bank_account_id, sample_check: sample_check} do
+      {:ok, created_check, _headers} =
+        Check.create(%{
+          description: sample_check.description,
+          to: test_address_id,
+          from: test_address_id,
+          bank_account: test_bank_account_id,
+          amount: 42
+        })
+
+        {:ok, deleted_check, _headers} = Check.delete(created_check.id)
+        assert deleted_check.id == created_check.id
+        assert deleted_check.deleted == true
+    end
+
+  end
+
+end
diff --git a/test/lob/letter_test.exs b/test/lob/letter_test.exs
new file mode 100644
index 0000000..e168511
--- /dev/null
+++ b/test/lob/letter_test.exs
@@ -0,0 +1,165 @@
+defmodule Lob.LetterTest do
+  use ExUnit.Case
+
+  alias Lob.Letter
+
+  setup do
+    sample_address = %{
+      name: "TestAddress",
+      email: "test@test.com",
+      address_line1: "185 Berry Street",
+      address_line2: "Suite 6100",
+      address_city: "San Francisco",
+      address_state: "CA",
+      address_country: "US",
+      address_zip: "94107"
+    }
+
+    sample_letter = %{
+      description: "Library Test Letter #{DateTime.utc_now |> DateTime.to_string}"
+    }
+
+    # TODO(anthony): Once address API is added to wrapper, replace this ID with a created address
+    %{
+      test_address_id: "adr_a7d78be7f746a0a7",
+      sample_address: sample_address,
+      sample_letter: sample_letter
+    }
+  end
+
+  describe "list/2" do
+
+    test "lists letters" do
+      {:ok, letters, _headers} = Letter.list()
+      assert letters.object == "list"
+    end
+
+    test "includes total count" do
+      {:ok, letters, _headers} = Letter.list(%{include: ["total_count"]})
+      assert Map.get(letters, :total_count) != nil
+    end
+
+    test "lists by limit" do
+      {:ok, letters, _headers} = Letter.list(%{limit: 2})
+      assert letters.count == 2
+    end
+
+    test "filters by metadata" do
+      {:ok, letters, _headers} = Letter.list(%{metadata: %{foo: "bar"}})
+      assert letters.count == 1
+    end
+
+  end
+
+  describe "retrieve/2" do
+
+    test "retrieves a letter", %{test_address_id: test_address_id, sample_letter: sample_letter} do
+      {:ok, created_letter, _headers} =
+        Letter.create(%{
+          description: sample_letter.description,
+          to: test_address_id,
+          from: test_address_id,
+          color: true,
+          file: "https://s3-us-west-2.amazonaws.com/lob-assets/letter-goblue.pdf"
+        })
+
+      {:ok, retrieved_letter, _headers} = Letter.retrieve(created_letter.id)
+      assert retrieved_letter.description == created_letter.description
+    end
+
+  end
+
+  describe "create/2" do
+
+    test "creates a letter with address_id", %{test_address_id: test_address_id, sample_letter: sample_letter} do
+      {:ok, created_letter, headers} =
+        Letter.create(%{
+          description: sample_letter.description,
+          to: test_address_id,
+          from: test_address_id,
+          color: true,
+          file: "https://s3-us-west-2.amazonaws.com/lob-assets/letter-goblue.pdf"
+        })
+
+      assert created_letter.description == sample_letter.description
+      assert Enum.member?(headers, {"X-Rate-Limit-Limit", "150"})
+    end
+
+    test "creates a letter with address params", %{sample_letter: sample_letter, sample_address: sample_address} do
+      {:ok, created_letter, headers} =
+        Letter.create(%{
+          description: sample_letter.description,
+          to: sample_address,
+          from: sample_address,
+          color: true,
+          file: "https://s3-us-west-2.amazonaws.com/lob-assets/letter-goblue.pdf"
+        })
+
+      assert created_letter.description == sample_letter.description
+      assert Enum.member?(headers, {"X-Rate-Limit-Limit", "150"})
+    end
+
+    test "creates a letter with file as PDF", %{test_address_id: test_address_id, sample_letter: sample_letter} do
+      {:ok, created_letter, headers} =
+        Letter.create(%{
+          description: sample_letter.description,
+          to: test_address_id,
+          from: test_address_id,
+          color: true,
+          file: %{local_path: "test/assets/8.5x11.pdf"}
+        })
+
+      assert created_letter.description == sample_letter.description
+      assert Enum.member?(headers, {"X-Rate-Limit-Limit", "150"})
+    end
+
+    test "creates a letter with an idempotency key", %{test_address_id: test_address_id, sample_letter: sample_letter} do
+      idempotency_key = UUID.uuid4()
+
+      {:ok, created_letter, _headers} =
+        Letter.create(%{
+          description: sample_letter.description,
+          to: test_address_id,
+          from: test_address_id,
+          color: true,
+          file: %{local_path: "test/assets/8.5x11.pdf"}
+        }, %{
+          "Idempotency-Key" => idempotency_key
+        })
+
+      {:ok, duplicated_letter, _headers} =
+        Letter.create(%{
+          description: "Duplicated Letter",
+          to: test_address_id,
+          from: test_address_id,
+          color: true,
+          file: %{local_path: "test/assets/8.5x11.pdf"}
+        }, %{
+          "Idempotency-Key" => idempotency_key
+        })
+
+      assert created_letter.description == duplicated_letter.description
+    end
+
+  end
+
+  describe "delete/2" do
+
+    test "deletes a letter", %{test_address_id: test_address_id, sample_letter: sample_letter} do
+      {:ok, created_letter, _headers} =
+        Letter.create(%{
+          description: sample_letter.description,
+          to: test_address_id,
+          from: test_address_id,
+          color: true,
+          file: %{local_path: "test/assets/8.5x11.pdf"}
+        })
+
+        {:ok, deleted_letter, _headers} = Letter.delete(created_letter.id)
+        assert deleted_letter.id == created_letter.id
+        assert deleted_letter.deleted == true
+    end
+
+  end
+
+end
diff --git a/test/lob/postcard_test.exs b/test/lob/postcard_test.exs
index ef6536a..43d142d 100644
--- a/test/lob/postcard_test.exs
+++ b/test/lob/postcard_test.exs
@@ -30,22 +30,22 @@ defmodule Lob.PostcardTest do
 
   describe "list/2" do
 
-    test "should list postcards" do
+    test "lists postcards" do
       {:ok, postcards, _headers} = Postcard.list()
       assert postcards.object == "list"
     end
 
-    test "should include total count" do
+    test "includes total count" do
       {:ok, postcards, _headers} = Postcard.list(%{include: ["total_count"]})
       assert Map.get(postcards, :total_count) != nil
     end
 
-    test "should list by limit" do
+    test "lists by limit" do
       {:ok, postcards, _headers} = Postcard.list(%{limit: 2})
       assert postcards.count == 2
     end
 
-    test "should filter by metadata" do
+    test "filters by metadata" do
       {:ok, postcards, _headers} = Postcard.list(%{metadata: %{foo: "bar"}})
       assert postcards.count == 1
     end
@@ -54,7 +54,7 @@ defmodule Lob.PostcardTest do
 
   describe "retrieve/2" do
 
-    test "should retrieve a postcard", %{test_address_id: test_address_id, sample_postcard: sample_postcard} do
+    test "retrieves a postcard", %{test_address_id: test_address_id, sample_postcard: sample_postcard} do
       {:ok, created_postcard, _headers} =
         Postcard.create(%{
           description: sample_postcard.description,
@@ -63,15 +63,15 @@ defmodule Lob.PostcardTest do
           back: "https://lob.com/postcardback.pdf"
         })
 
-        {:ok, retrieved_postcard, _headers} = Postcard.retrieve(created_postcard.id)
-        assert retrieved_postcard.description == created_postcard.description
+      {:ok, retrieved_postcard, _headers} = Postcard.retrieve(created_postcard.id)
+      assert retrieved_postcard.description == created_postcard.description
     end
 
   end
 
   describe "create/2" do
 
-    test "should create a postcard with address_id", %{test_address_id: test_address_id, sample_postcard: sample_postcard} do
+    test "creates a postcard with address_id", %{test_address_id: test_address_id, sample_postcard: sample_postcard} do
       {:ok, created_postcard, headers} =
         Postcard.create(%{
           description: sample_postcard.description,
@@ -84,7 +84,7 @@ defmodule Lob.PostcardTest do
       assert Enum.member?(headers, {"X-Rate-Limit-Limit", "150"})
     end
 
-    test "should create a postcard with to address params", %{sample_postcard: sample_postcard, sample_address: sample_address} do
+    test "creates a postcard with to address params", %{sample_postcard: sample_postcard, sample_address: sample_address} do
       {:ok, created_postcard, headers} =
         Postcard.create(%{
           description: sample_postcard.description,
@@ -97,7 +97,7 @@ defmodule Lob.PostcardTest do
       assert Enum.member?(headers, {"X-Rate-Limit-Limit", "150"})
     end
 
-    test "should create a postcard with from address params", %{test_address_id: test_address_id, sample_postcard: sample_postcard, sample_address: sample_address} do
+    test "creates a postcard with from address params", %{test_address_id: test_address_id, sample_postcard: sample_postcard, sample_address: sample_address} do
       {:ok, created_postcard, headers} =
         Postcard.create(%{
           description: sample_postcard.description,
@@ -111,7 +111,7 @@ defmodule Lob.PostcardTest do
       assert Enum.member?(headers, {"X-Rate-Limit-Limit", "150"})
     end
 
-    test "should create a postcard with front and back as urls", %{test_address_id: test_address_id, sample_postcard: sample_postcard} do
+    test "creates a postcard with front and back as urls", %{test_address_id: test_address_id, sample_postcard: sample_postcard} do
       {:ok, created_postcard, headers} =
         Postcard.create(%{
           description: sample_postcard.description,
@@ -124,7 +124,7 @@ defmodule Lob.PostcardTest do
       assert Enum.member?(headers, {"X-Rate-Limit-Limit", "150"})
     end
 
-    test "should create a postcard with front and back as PDFs", %{test_address_id: test_address_id, sample_postcard: sample_postcard} do
+    test "creates a postcard with front and back as PDFs", %{test_address_id: test_address_id, sample_postcard: sample_postcard} do
       {:ok, created_postcard, headers} =
         Postcard.create(%{
           description: sample_postcard.description,
@@ -137,7 +137,7 @@ defmodule Lob.PostcardTest do
       assert Enum.member?(headers, {"X-Rate-Limit-Limit", "150"})
     end
 
-    test "should create a postcard with an idempotency key", %{test_address_id: test_address_id, sample_postcard: sample_postcard} do
+    test "creates a postcard with an idempotency key", %{test_address_id: test_address_id, sample_postcard: sample_postcard} do
       idempotency_key = UUID.uuid4()
 
       {:ok, created_postcard, _headers} =
@@ -167,7 +167,7 @@ defmodule Lob.PostcardTest do
 
   describe "delete/2" do
 
-    test "should destroy a postcard", %{test_address_id: test_address_id, sample_postcard: sample_postcard} do
+    test "deletes a postcard", %{test_address_id: test_address_id, sample_postcard: sample_postcard} do
       {:ok, created_postcard, _headers} =
         Postcard.create(%{
           description: sample_postcard.description,