diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index eb2268157b011..3384012c49108 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -159,7 +159,7 @@ def valid_type?(type)
       end
 
       # Returns 62. SQLite supports index names up to 64
-      # characters. The rest is used by rails internally to perform
+      # characters. The rest is used by Rails internally to perform
       # temporary rename operations
       def allowed_index_name_length
         index_name_length - 2
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index 98ea425d169b1..2c0ca62924d1b 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -3,7 +3,7 @@
 require "active_model/railtie"
 
 # For now, action_controller must always be present with
-# rails, so let's make sure that it gets required before
+# Rails, so let's make sure that it gets required before
 # here. This is needed for correctly setting up the middleware.
 # In the future, this might become an optional require.
 require "action_controller/railtie"
diff --git a/guides/source/plugins.md b/guides/source/plugins.md
index 8f055f8fe3962..ff84861b8c878 100644
--- a/guides/source/plugins.md
+++ b/guides/source/plugins.md
@@ -30,7 +30,7 @@ Setup
 -----
 
 Currently, Rails plugins are built as gems, _gemified plugins_. They can be shared across
-different rails applications using RubyGems and Bundler if desired.
+different Rails applications using RubyGems and Bundler if desired.
 
 ### Generate a gemified plugin.
 
diff --git a/guides/source/security.md b/guides/source/security.md
index ca985134e6b67..2d1bc3b5b3295 100644
--- a/guides/source/security.md
+++ b/guides/source/security.md
@@ -249,7 +249,7 @@ There are many other possibilities, like using a `<script>` tag to make a cross-
 
 Note: We can't distinguish a `<script>` tag's origin—whether it's a tag on your own site or on some other malicious site—so we must block all `<script>` across the board, even if it's actually a safe same-origin script served from your own site. In these cases, explicitly skip CSRF protection on actions that serve JavaScript meant for a `<script>` tag.
 
-To protect against all other forged requests, we introduce a _required security token_ that our site knows but other sites don't know. We include the security token in requests and verify it on the server. This is a one-liner in your application controller, and is the default for newly created rails applications:
+To protect against all other forged requests, we introduce a _required security token_ that our site knows but other sites don't know. We include the security token in requests and verify it on the server. This is a one-liner in your application controller, and is the default for newly created Rails applications:
 
 ```ruby
 protect_from_forgery with: :exception
diff --git a/railties/lib/rails.rb b/railties/lib/rails.rb
index fe789f3c2aa71..c024fb66416c7 100644
--- a/railties/lib/rails.rb
+++ b/railties/lib/rails.rb
@@ -52,7 +52,7 @@ def backtrace_cleaner
       end
     end
 
-    # Returns a Pathname object of the current rails project,
+    # Returns a Pathname object of the current Rails project,
     # otherwise it returns nil if there is no project:
     #
     #   Rails.root
@@ -77,7 +77,7 @@ def env=(environment)
       @_env = ActiveSupport::StringInquirer.new(environment)
     end
 
-    # Returns all rails groups for loading based on:
+    # Returns all Rails groups for loading based on:
     #
     # * The Rails environment;
     # * The environment variable RAILS_GROUPS;
@@ -100,7 +100,7 @@ def groups(*groups)
     end
 
     # Returns a Pathname object of the public folder of the current
-    # rails project, otherwise it returns nil if there is no project:
+    # Rails project, otherwise it returns nil if there is no project:
     #
     #   Rails.public_path
     #     # => #<Pathname:/Users/someuser/some/path/project/public>
diff --git a/railties/lib/rails/generators/rails/app/templates/config/databases/postgresql.yml b/railties/lib/rails/generators/rails/app/templates/config/databases/postgresql.yml
index bd5c0b10f6417..145cfb7f74632 100644
--- a/railties/lib/rails/generators/rails/app/templates/config/databases/postgresql.yml
+++ b/railties/lib/rails/generators/rails/app/templates/config/databases/postgresql.yml
@@ -17,7 +17,7 @@
 default: &default
   adapter: postgresql
   encoding: unicode
-  # For details on connection pooling, see rails configuration guide
+  # For details on connection pooling, see Rails configuration guide
   # http://guides.rubyonrails.org/configuring.html#database-pooling
   pool: <%%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
 
diff --git a/railties/test/application/rackup_test.rb b/railties/test/application/rackup_test.rb
index 9fdd2d6bd9620..4aef9b299cc88 100644
--- a/railties/test/application/rackup_test.rb
+++ b/railties/test/application/rackup_test.rb
@@ -18,7 +18,7 @@ def teardown
       teardown_app
     end
 
-    test "rails app is present" do
+    test "Rails app is present" do
       assert File.exist?(app_path("config"))
     end
 
diff --git a/railties/test/isolation/abstract_unit.rb b/railties/test/isolation/abstract_unit.rb
index 032c245c3aa20..5528459ad217b 100644
--- a/railties/test/isolation/abstract_unit.rb
+++ b/railties/test/isolation/abstract_unit.rb
@@ -1,7 +1,7 @@
 # Note:
 # It is important to keep this file as light as possible
 # the goal for tests that require this is to test booting up
-# rails from an empty state, so anything added here could
+# Rails from an empty state, so anything added here could
 # hide potential failures
 #
 # It is also good to know what is the bare minimum to get