The chapter begins by introducing what classification is and why is it important for human society, including the role that classification has in our ability to interpret the reality of the world. This chapter is philosophical in nature and designed to affirm that people have always classified objects in their environment, including words and language. We cannot escape examination of classification if we hope to understand our world, and especially the world of plant diversity, which is a cornerstone for human survival. This chapter gives a quick overview of some of the changes in classification that have transpired during the past 2000 years, in effect an encapsulation of what lies ahead in the rest of the book.