The three main categories are:

1. Creational Patterns: Deal with object creation mechanisms, trying to create objects in a manner suitable to the situation (e.g., Singleton, Factory, Builder)

2. Structural Patterns: Deal with object composition and relationships between entities (e.g., Adapter, Decorator, Facade)

3. Behavioral Patterns: Focus on communication between objects and the assignment of responsibilities (e.g., Observer, Strategy, Command)