Design patterns are reusable solutions to common software design problems. They provide standardized approaches to solving specific types of challenges in software development. Here are some main design patterns categorized into three groups: Creational, Structural, and Behavioral.

Creational Design Patterns:

1. Singleton: Ensures a class has only one instance and provides a global point of access to that instance.
2. Factory Method: Defines an interface for creating objects, but allows subclasses to decide which class to instantiate.
3. Abstract Factory: Provides an interface for creating families of related or dependent objects without specifying their concrete classes.
4. Builder: Separates the construction of a complex object from its representation, allowing the same construction process to create different representations.
5. Prototype: Creates new objects by copying an existing object, allowing for efficient object creation and customization.

Structural Design Patterns:

1. Adapter: Allows objects with incompatible interfaces to work together by providing a wrapper that translates one interface into another.
2. Bridge: Separates abstraction from implementation, allowing both to evolve independently.
3. Composite: Represents objects in a tree structure, allowing clients to treat individual objects and compositions of objects uniformly.
4. Decorator: Dynamically adds responsibilities to objects, providing a flexible alternative to subclassing for extending functionality.
5. Facade: Provides a unified interface to a set of interfaces in a subsystem, simplifying its usage.
6. Flyweight: Shares objects to reduce memory usage by allowing multiple objects to share the same data.

Behavioral Design Patterns:

1. Chain of Responsibility: Creates a chain of receiver objects to handle requests, allowing the request to be passed along the chain until it’s handled.
2. Command: Encapsulates a request as an object, allowing parameterization of clients with different requests, queuing, and logging of requests.
3. Interpreter: Provides a way to evaluate language grammar or expressions, suitable for domain-specific languages.
4. Iterator: Provides a way to access elements of a collection sequentially without exposing its underlying representation.
5. Mediator: Defines an object that encapsulates communication between objects in a system, reducing dependencies.
6. Memento: Allows capturing an object’s internal state and restoring it to that state later, without exposing its structure.
7. Observer: Defines a dependency between objects so that when one object changes state, its dependents are notified and updated automatically.
8. State: Allows an object to change its behavior when its internal state changes.
9. Strategy: Defines a family of algorithms, encapsulates each one, and makes them interchangeable.
10. Template Method: Defines the structure of an algorithm in a superclass but allows subclasses to override specific steps.
11. Visitor: Lets you add further operations to objects without having to modify them, following the open-closed principle.

Each of these design patterns addresses specific design challenges and promotes best practices in software development. However, it’s important to choose the appropriate design pattern based on the problem you’re trying to solve and the characteristics of your application.