To face the challenges of increasing demand for variety, more specific customer demands and shortening product life cycles, firms increasingly adopt mass customization techniques. Two important such techniques are product modularization and product platform development, which allow firms to reach high levels of product variety, and at the same time, keep complexity and its related costs at a limited level. Often modularization and product platform development are treated as variants of the same basic idea. However, even if the concepts are closely related, they also have some fundamental differences, which influence their usefulness and applicability in different settings. One potential shortcoming of existing literature on modularization and product platforms is the present lack of research on their limitations and potential negative effects. Therefore, the purpose of this paper is to identify and explore contingencies influencing the applicability of modularization and product platforms, respectively, taking their different economic effects as a starting point. Moreover, the paper addresses how different organizing solutions are interrelated with the use of modularization and product platform approaches. The empirical observations originate from studies of three Swedish manufacturing firms. The study reveals that important contingencies affecting the applicability of modularization and product platforms are demand side characteristics and the speed of environmental change. Furthermore, it is seen that firms need to organize themselves differently with respect to how they combine modularization and platforms, for example, in terms of degree of centralization, formalization, and allocation of decision-making authority, and that this poses challenges to the combined use of the two approaches.