diff --git a/.gitignore b/.gitignore
index b642bc1..694cdb3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,6 @@
+# byebug generated
+.byebug_history
+
 # rcov generated
 coverage
 coverage.data
diff --git a/lib/quaderno-ruby.rb b/lib/quaderno-ruby.rb
index 0e0ae26..12d40db 100644
--- a/lib/quaderno-ruby.rb
+++ b/lib/quaderno-ruby.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Quaderno
 end
 
@@ -10,4 +12,4 @@ class Quaderno
 require 'quaderno-ruby/collection'
 
 %w(block crud deliver payment retrieve).each { |filename| require "quaderno-ruby/behavior/#{filename}" }
-%w(base contact item invoice receipt credit income estimate expense recurring document_item report report_request evidence payment webhook tax checkout_session).each { |filename| require "quaderno-ruby/#{ filename }" }
+%w(base contact item transaction invoice receipt credit income estimate expense recurring document_item report report_request evidence payment webhook tax checkout_session).each { |filename| require "quaderno-ruby/#{filename}" }
diff --git a/lib/quaderno-ruby/base.rb b/lib/quaderno-ruby/base.rb
index ac62690..d6d534b 100644
--- a/lib/quaderno-ruby/base.rb
+++ b/lib/quaderno-ruby/base.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'httparty'
 require 'json'
 
diff --git a/lib/quaderno-ruby/behavior/crud.rb b/lib/quaderno-ruby/behavior/crud.rb
index 23bc846..f11f54b 100644
--- a/lib/quaderno-ruby/behavior/crud.rb
+++ b/lib/quaderno-ruby/behavior/crud.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Quaderno::Behavior
   module Crud
 
@@ -69,7 +71,7 @@ def find(id, options = {})
 
       def create(params = {})
         authentication = get_authentication(params.merge(api_model: api_model))
-        params.dup.delete_if { |k,v| %w(auth_token access_token api_url mode api_model').include? k.to_s }
+        params.dup.delete_if { |k, _| %w[auth_token access_token api_url mode api_model].include? k.to_s }
 
         response = post("#{authentication[:url]}#{api_model.api_path}.json",
           body: params.to_json,
@@ -91,7 +93,7 @@ def create(params = {})
 
       def update(id, params = {})
         authentication = get_authentication(params.merge(api_model: api_model))
-        params = params.dup.delete_if { |k,v| %w(auth_token access_token api_url mode api_model').include? k.to_s }
+        params = params.dup.delete_if { |k, _| %w[auth_token access_token api_url mode api_model].include? k.to_s }
 
         response = put("#{authentication[:url]}#{api_model.api_path}/#{id}.json",
           body: params.to_json,
@@ -114,7 +116,7 @@ def update(id, params = {})
       def delete(id, options = {})
         authentication = get_authentication(options.merge(api_model: api_model))
 
-        response = HTTParty.delete("#{authentication[:url]}#{ api_model.api_path }/#{ id }.json",
+        response = HTTParty.delete("#{authentication[:url]}#{api_model.api_path}/#{id}.json",
           basic_auth: authentication[:basic_auth],
           headers: default_headers.merge(authentication[:headers])
         )
diff --git a/lib/quaderno-ruby/transaction.rb b/lib/quaderno-ruby/transaction.rb
new file mode 100644
index 0000000..1a61d79
--- /dev/null
+++ b/lib/quaderno-ruby/transaction.rb
@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class Quaderno::Transaction < Quaderno::Base
+  api_model Quaderno::Transaction
+  api_path 'transactions'
+  is_a_document? true
+
+  class << self
+    undef :all, :find, :update, :delete
+  end
+end
diff --git a/lib/quaderno-ruby/version.rb b/lib/quaderno-ruby/version.rb
index 160187c..6c7ecc6 100644
--- a/lib/quaderno-ruby/version.rb
+++ b/lib/quaderno-ruby/version.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Quaderno
-  VERSION = "2.1.3"
+  VERSION = "2.2.0"
 end
diff --git a/quaderno.gemspec b/quaderno.gemspec
index 71eda56..14c58bd 100644
--- a/quaderno.gemspec
+++ b/quaderno.gemspec
@@ -24,7 +24,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency('httparty', '~> 0.21.0')
   spec.add_development_dependency('rdoc', '>= 6.3.1')
   spec.add_development_dependency('activesupport', '~> 4.2.0')
-  spec.add_development_dependency('webmock', '~> 1.22.6')
+  spec.add_development_dependency('webmock', '~> 3.18')
   spec.add_development_dependency('vcr', '>= 0')
   spec.add_development_dependency('bundler', '~> 2.2')
   spec.add_development_dependency('rake', '>= 12.3.3')
diff --git a/spec/helper.rb b/spec/helper.rb
index d6802df..9ec4e57 100644
--- a/spec/helper.rb
+++ b/spec/helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 $LOAD_PATH.unshift(File.join(File.dirname(__FILE__), '..', 'lib'))
 $LOAD_PATH.unshift File.expand_path('../../lib', __FILE__)
 $LOAD_PATH.unshift(File.dirname(__FILE__))
@@ -17,4 +19,3 @@
 TEST_KEY = 'sk_test_bMz9mJJ5bZnWPwWGuV8y'
 TEST_OAUTH_ACCESS_TOKEN = 'afa16c7478f0ba3be222e627c2571d4dd5dca47924996b13a3af377feca47ff0'
 OLDEST_SUPPORTED_API_VERSION = 20160602
-
diff --git a/spec/unit/test_quaderno_transaction.rb b/spec/unit/test_quaderno_transaction.rb
new file mode 100644
index 0000000..8c23c99
--- /dev/null
+++ b/spec/unit/test_quaderno_transaction.rb
@@ -0,0 +1,97 @@
+# frozen_string_literal: true
+
+require 'helper'
+
+describe Quaderno::Transaction do
+  context 'A user with an authentication token' do
+    before(:each) do
+      Quaderno::Base.configure do |config|
+        config.auth_token = TEST_KEY
+        config.url = TEST_URL
+        config.api_version = nil
+      end
+    end
+
+    it 'should create a sale transaction' do
+      sale_params = {
+        type: 'sale', customer: { first_name: 'John', last_name: 'Smith', email: 'an_email@example.com' },
+        evidence: { billing_country: 'US', ip_address: '255.255.255.255', bank_country: 'US' },
+        currency: 'USD',
+        items: [
+          {
+            description: 'Awesome ebook', quantity: 1, amount: 19,
+            tax: {
+              city: nil, country: 'US', county: nil, currency: 'USD', name: nil, notes: nil,
+              notice: '', product_type: 'service', rate: 0.0, region: 'NY', tax_behavior: 'exclusive',
+              tax_code: 'ebook', taxable_part: nil, import: true, subtotal: nil, tax_amount: nil, total_amount: nil
+            }
+          },
+          {
+            description: 'Awesome SaaS', quantity: 1, amount: 89,
+            tax: {
+              city: 'NEW YORK', country: 'US', county: 'NEW YORK', currency: 'USD', name: 'Sales tax', notes: nil,
+              notice: '', product_type: 'service', rate: 8.875, region: 'NY', tax_behavior: 'exclusive',
+              tax_code: 'saas', taxable_part: 100.0, import: true, subtotal: nil, tax_amount: nil, total_amount: nil
+            }
+          }
+        ],
+        payment: { method: 'credit_card', processor: 'processor12345', processor_id: 'txn_12345' },
+        processor: 'processor12345', processor_id: 'txn_12345', po_number: 'PO_12345',
+        tags: 'tag-a,tag-b,tag-c',
+        custom_metadata: { anything_you_want: 'extra info' }
+      }
+
+      VCR.use_cassette('new sale') do
+        @transaction = Quaderno::Transaction.create(sale_params)
+      end
+
+      expect(@transaction.is_a?(Quaderno::Transaction)).to be true
+      expect(@transaction.type).to eq 'Invoice'
+      expect(@transaction.currency).to eq sale_params[:currency]
+      expect(@transaction.items.count).to eq sale_params[:items].count
+      expect(@transaction.total_cents).to eq(sale_params[:items].sum { |item| item[:amount] * 100 })
+      expect(@transaction.contact.full_name).to eq "#{sale_params[:customer][:first_name]} #{sale_params[:customer][:last_name]}"
+    end
+
+    it 'should create a refund transaction' do
+      refund_params = {
+        type: 'refund', customer: { first_name: 'John', last_name: 'Smith', email: 'an_email@example.com' },
+        evidence: { billing_country: 'US', ip_address: '255.255.255.255', bank_country: 'US' },
+        currency: 'USD',
+        items: [
+          {
+            description: 'Awesome ebook', quantity: 1, amount: 19,
+            tax: {
+              city: nil, country: 'US', county: nil, currency: 'USD', name: nil, notes: nil,
+              notice: '', product_type: 'service', rate: 0.0, region: 'NY', tax_behavior: 'exclusive',
+              tax_code: 'ebook', taxable_part: nil, import: true, subtotal: nil, tax_amount: nil, total_amount: nil
+            }
+          },
+          {
+            description: 'Awesome SaaS', quantity: 1, amount: 89,
+            tax: {
+              city: 'NEW YORK', country: 'US', county: 'NEW YORK', currency: 'USD', name: 'Sales tax', notes: nil,
+              notice: '', product_type: 'service', rate: 8.875, region: 'NY', tax_behavior: 'exclusive',
+              tax_code: 'saas', taxable_part: 100.0, import: true, subtotal: nil, tax_amount: nil, total_amount: nil
+            }
+          }
+        ],
+        payment: { method: 'credit_card', processor: 'processor12345', processor_id: 'txn_12345' },
+        processor: 'processor12345', processor_id: 'txn_12345', po_number: 'PO_12345',
+        tags: 'tag-a,tag-b,tag-c',
+        custom_metadata: { anything_you_want: 'extra info' }
+      }
+
+      VCR.use_cassette('new refund') do
+        @transaction = Quaderno::Transaction.create(refund_params)
+      end
+
+      expect(@transaction.is_a?(Quaderno::Transaction)).to be true
+      expect(@transaction.type).to eq 'Credit'
+      expect(@transaction.currency).to eq refund_params[:currency]
+      expect(@transaction.items.count).to eq refund_params[:items].count
+      expect(@transaction.total_cents).to eq(refund_params[:items].sum { |item| item[:amount] * 100 })
+      expect(@transaction.contact.full_name).to eq "#{refund_params[:customer][:first_name]} #{refund_params[:customer][:last_name]}"
+    end
+  end
+end