Design patterns are reusable solutions to commonly occurring problems in software design. They represent best practices and proven solutions that have evolved over time. Design patterns are important because they:

• Provide a common vocabulary for developers
• Reduce development time by offering tested solutions
• Improve code maintainability and readability
• Promote loose coupling and high cohesion
• Help avoid common design pitfalls

The concept was popularized by the "Gang of Four" (GoF) book which categorized 23 fundamental patterns into Creational, Structural, and Behavioral categories.