Observer
Notifying dependents of state changes.
Strategy
Encapsulating interchangeable algorithms.
Template Method
Defining algorithm skeleton with customizable steps.
Command
Encapsulating requests as objects.
Iterator
Traversing collections without exposing internals.
State
Alter behavior when internal state changes.
Mediator
Centralize complex communications.
Memento
Capture and restore object state.
Visitor
Separate algorithm from object structure.
Chain of Responsibility
Pass request along handler chain.
Interpreter
Define grammar and interpret sentences.