||This thesis introduces Product Architecture Network as a representation model for modular product architectures that enables product variety within product families for mass customization. The main feature of this representation is the integration of a discrete model of product variety based on graphs and graph-theoretical descriptors which cohesively encapsulates object-oriented modeling principles and notations. Graph theory and object-oriented representations have both been well developed and applied in numerous engineering disciplines. The difference between these approaches can be characterized as how they define a set of variants in a variety space. Graphs are combinatorial structures which represent combinatorial design spaces, while objects characterize discretized entities with parameters, hence representing parametric design spaces. For modular products, a basic premise is the separation of visible and hidden information as well as the possibility of module interconnectivity through compatible interfaces. As modular and configurable products involve both parametric module configuration and a configuration synthesis of connecting different modules through interfaces, modular product families exhibit both parametric as well as combinatorial design spaces. Through an integrated application graph and object representations, these two types of variety spaces that coexist in modular products can be represented as a single, unified model. The approach is demonstrated with a number of case studies and implemented as a prototype system.