diff --git a/actionview/lib/action_view/helpers/date_helper.rb b/actionview/lib/action_view/helpers/date_helper.rb
index 61ce1d36e0ae7ffc71c703f81e0529c5d42e139e..04c5fd42186492f8ee975f240d16b36984adaf70 100644
--- a/actionview/lib/action_view/helpers/date_helper.rb
+++ b/actionview/lib/action_view/helpers/date_helper.rb
@@ -303,7 +303,7 @@ def date_select(object_name, method, options = {}, html_options = {})
       #   # the sunrise attribute.
       #   time_select("article", "start_time", include_seconds: true)
       #
-      #   # You can set the <tt>:minute_step</tt> to 15 which will give you: 00, 15, 30 and 45.
+      #   # You can set the <tt>:minute_step</tt> to 15 which will give you: 00, 15, 30, and 45.
       #   time_select 'game', 'game_time', {minute_step: 15}
       #
       #   # Creates a time select tag with a custom prompt. Use <tt>prompt: true</tt> for generic prompts.
diff --git a/activesupport/lib/active_support/time_with_zone.rb b/activesupport/lib/active_support/time_with_zone.rb
index be2fceb1230a60bd3333a8ba98eccde525e4d76a..f7586efe6a1f61d8c74e043d1044de2cfd839202 100644
--- a/activesupport/lib/active_support/time_with_zone.rb
+++ b/activesupport/lib/active_support/time_with_zone.rb
@@ -133,7 +133,7 @@ def zone
       period.zone_identifier.to_s
     end
 
-    # Returns a string of the object's date, time, zone and offset from UTC.
+    # Returns a string of the object's date, time, zone, and offset from UTC.
     #
     #   Time.zone.now.inspect # => "Thu, 04 Dec 2014 11:00:25 EST -05:00"
     def inspect
diff --git a/guides/source/active_record_querying.md b/guides/source/active_record_querying.md
index 644756906a9de1670df734fc8825935878c8c3ab..bbe1b0decc8be5caf730f6de08c85ba2ba965115 100644
--- a/guides/source/active_record_querying.md
+++ b/guides/source/active_record_querying.md
@@ -50,7 +50,7 @@ class Role < ApplicationRecord
 end
 ```
 
-Active Record will perform queries on the database for you and is compatible with most database systems, including MySQL, MariaDB, PostgreSQL and SQLite. Regardless of which database system you're using, the Active Record method format will always be the same.
+Active Record will perform queries on the database for you and is compatible with most database systems, including MySQL, MariaDB, PostgreSQL, and SQLite. Regardless of which database system you're using, the Active Record method format will always be the same.
 
 Retrieving Objects from the Database
 ------------------------------------
diff --git a/guides/source/engines.md b/guides/source/engines.md
index 83c0a7f337afe6ffcaee64571c019acd3e4a0dc4..0020112a1ce368af1cc5d5d624e6159911e74876 100644
--- a/guides/source/engines.md
+++ b/guides/source/engines.md
@@ -184,7 +184,7 @@ end
 By inheriting from the `Rails::Engine` class, this gem notifies Rails that
 there's an engine at the specified path, and will correctly mount the engine
 inside the application, performing tasks such as adding the `app` directory of
-the engine to the load path for models, mailers, controllers and views.
+the engine to the load path for models, mailers, controllers, and views.
 
 The `isolate_namespace` method here deserves special notice. This call is
 responsible for isolating the controllers, models, routes and other things into
diff --git a/guides/source/layouts_and_rendering.md b/guides/source/layouts_and_rendering.md
index 2722789c4990f618a2b56d21f78a42f78e992b5c..ad8ec150711d25f4dc77c98ef59e824454144e6b 100644
--- a/guides/source/layouts_and_rendering.md
+++ b/guides/source/layouts_and_rendering.md
@@ -749,7 +749,7 @@ When Rails renders a view as a response, it does so by combining the view with t
 
 ### Asset Tag Helpers
 
-Asset tag helpers provide methods for generating HTML that link views to feeds, JavaScript, stylesheets, images, videos and audios. There are six asset tag helpers available in Rails:
+Asset tag helpers provide methods for generating HTML that link views to feeds, JavaScript, stylesheets, images, videos, and audios. There are six asset tag helpers available in Rails:
 
 * `auto_discovery_link_tag`
 * `javascript_include_tag`
diff --git a/railties/lib/rails/engine.rb b/railties/lib/rails/engine.rb
index 86d66afddbf58942950db8281f4c5dfadcd69557..90e7c04d7c83aacf02b46492b2f5ae721e855cb8 100644
--- a/railties/lib/rails/engine.rb
+++ b/railties/lib/rails/engine.rb
@@ -337,7 +337,7 @@ module Rails
   # == Loading priority
   #
   # In order to change engine's priority you can use +config.railties_order+ in the main application.
-  # It will affect the priority of loading views, helpers, assets and all the other files
+  # It will affect the priority of loading views, helpers, assets, and all the other files
   # related to engine or application.
   #
   #   # load Blog::Engine with highest priority, followed by application and other railties
diff --git a/railties/lib/rails/paths.rb b/railties/lib/rails/paths.rb
index 88ec2ba85b1e2605ecd7d2c46300c73d336a537e..1c1810dde6e0f2212776273b045ef463762a4815 100644
--- a/railties/lib/rails/paths.rb
+++ b/railties/lib/rails/paths.rb
@@ -30,7 +30,7 @@ module Paths
     #   root["config/routes"].inspect # => ["config/routes.rb"]
     #
     # The +add+ method accepts the following options as arguments:
-    # eager_load, autoload, autoload_once and glob.
+    # eager_load, autoload, autoload_once, and glob.
     #
     # Finally, the +Path+ object also provides a few helpers:
     #