Patterns are systematic approaches to documenting and classifying recurrent problems and their solutions. Patterns are usually based on empirical observations of good practices. This chapter provides a brief introduction to the core concepts of patterns, and distinguishes between patterns in the real world, patterns in the heads of designers, and pattern descriptions. It starts with basic definitions and explains the relationship between context, problems, forces, and solutions. Key concepts such as connecting patterns into pattern languages, finding whole forms, and sharing best practices among peers are elaborated. To distinguish between patterns in the world, in the heads of designers and in documentations it introduces a vocabulary that may clarify the different meanings of the term “pattern” in the context of design. A discussion of how patterns are recognized and induced by practitioners resolves why there are patterns at different levels of granularity and abstraction. Schema theory provides a theoretical framework to understand how successful strategies of problem solving are stored in the mind of an expert. To share this knowledge, patterns can be described in various ways using different pattern formats or templates. While there are many benefits of the pattern approach, both the pattern author and the pattern user face some challenges. Therefore some of the major benefits and challenges are discussed at the end of the chapter.