This chapter introduces the book’s central aim: to define and assess Chinese syntactic complexity using TC-units. It begins by exploring the multidimensional nature of syntactic complexity and reviews key principles of measurement in second language acquisition, drawing on the framework for understanding and executing measurement in SLA research by Norris and Ortega (2003). The chapter then examines the unique challenges posed by the structural features of Chinese for syntactic complexity analysis. In response, it proposes TC-units as a language-specific unit better suited to capturing Chinese discourse patterns. Finally, the chapter concludes with an outline of the six chapters.