In this paper two classes of clustering models are considered: (1) matrix, and (2) integer programming. The relationship between the matrix model, thep-median model and the classical group technology concept is discussed. A generalized group technology concept, based on generation for one part of a number of different process plans, is proposed. This new concept improves the quality of process (part) families and machine cells. A corresponding integer programming model is formulated. The models discussed are illustrated with numerical examples.