diff --git a/ruby/change-notes/2021-12-07-customizations.md b/ruby/change-notes/2021-12-07-customizations.md
new file mode 100644
index 00000000000..d15d9abd952
--- /dev/null
+++ b/ruby/change-notes/2021-12-07-customizations.md
@@ -0,0 +1,2 @@
+lgtm,codescanning
+* A new library, `Customizations.qll`, has been added, which allows for global customizations that affect all queries.
diff --git a/ruby/ql/lib/Customizations.qll b/ruby/ql/lib/Customizations.qll
new file mode 100644
index 00000000000..9b7fc73c31f
--- /dev/null
+++ b/ruby/ql/lib/Customizations.qll
@@ -0,0 +1,12 @@
+/**
+ * Contains customizations to the standard library.
+ *
+ * This module is imported by `ruby.qll`, so any customizations defined here automatically
+ * apply to all queries.
+ *
+ * Typical examples of customizations include adding new subclasses of abstract classes such as
+ * `FileSystemAccess`, or the `Source` and `Sink` classes associated with the security queries
+ * to model frameworks that are not covered by the standard library.
+ */
+
+import ruby
diff --git a/ruby/ql/lib/ruby.qll b/ruby/ql/lib/ruby.qll
index 18468c9f8cf..9d35b7bdc28 100644
--- a/ruby/ql/lib/ruby.qll
+++ b/ruby/ql/lib/ruby.qll
@@ -1 +1,6 @@
+/**
+ * Provides classes for working with Ruby programs.
+ */
+
+import Customizations
 import codeql.ruby.AST