Classification of individuals into distinct groups is one of the focal subjects implied by the person approach. Generically, classification has a broad domain of reference that stretches across many disciplines, including psychology. The relevance of classification to the person approach has been presented elsewhere (chap. 3), and it was also concluded that other strategies implementing that approach are possible. However, the longitudinal multivariate strategy of investigation on which we rely in this book, with its focus on types, states, individual stability, structural stability, and so on, seems to us to be naturally realized in connection with classificatory concepts and methods. Of course, within a classificatory paradigm, several methodologies arealso possible; the central issues and concepts usually remain isomorphic across these methodologies. For our purpose, we focus on cluster analysis and on methods derived from a cluster analytical view. In this chapter, we restriet our attention to cross-sectional classification, which in later chapters is used as a building block for longitudinal analyses.