There are 23 design patterns classified into 3 categories:
1. Creational Design Pattern
i. Factory Method
ii. Abstract Factory
iii. Builder
iv. Prototype
v. Singleton
2. Structural Design Patterns
i. Adapter
ii. Bridge
iii. Composite
iv. Decorator
v. Façade
vi. Flyweight
vii. Proxy
3. Behavioral Design Patterns
i. Chain of Responsibility
ii. Command
iii. Interpreter
iv. Iterator
v. Mediator
vi. Memento
vii. Observer
viii. State
ix. Strategy
x. Visitor
xi. Template Method