This chapter describes the concept of a Pattern, and describes why patterns are the basis of knowledge. It establishes the semantics of Pattern, and describes the concept of “information space”, an abstract arena in which patterns of information create meanings. It shows how the concept of measurability is the basis of all meaning, and how meanings are structured by patterns in information space. It also distinguishes a meaning from its physical representation and establishes the identity between objects and patterns. It shows how joining and constraining meanings creates new patterns of information, which lead to new meanings, and hence the ability to configure meanings from other meanings. This is the basis on which components of knowledge are derived in this book, and also in its companions in the series.