This chapter, Boundaries of Knowledge, discusses knowledge boundaries. Knowledge boundaries determine the ease and feasibility of sharing knowledge between different groups of individuals. The concept of a knowledge boundary is fleshed out, and different types of knowledge boundaries are identified, which can range in complexity and in the ease or difficulty in understanding and sharing a common language and a common knowledge. Different techniques for navigating the types of knowledge boundaries are discussed, using examples that are drawn from practical intelligence community experiences. As a way to illustrate the difference between the academic and intelligence communities and allude to the communication challenges faced, examples of five climate-related and analytically related concepts are compared. The examples cover situations when definitions of a concept are the same but the meanings are different, when definitions of a concept are the same and the meanings are the same, when definitions are different but the meanings are the same, when definitions are different and the meanings are different, and when a comparison is not possible. The chapter concludes with implications for the two communities to reach common ground.