Modularity in product architecture and its importance in product development has become a critical discussion topic in the last few decades. Several Product Modularity definitions and prospects were discussed by many researchers, however, most of the definitions and concepts are proliferated such that it is difficult to apply one universal definition to every modular product architecture and in product development. Automotive seat modular design and key factors for consideration towards modular seat design and assemblies are the main objectives of this work. The primary objectives are focused around the most “natural segmentation” of the seat elements (i.e., cushions, backs, trims, plastics, head restraints, etc.) to enable the greatest ease of final assembly and greatest flexibility for scalable feature offerings around common assembly “hard-points.” Additionally, modular design disciplines enable a “lean” design approach that standardizes assembly, parts, and Bill of Process for the greatest efficiencies. A comparison of integrated seat system design and assembly versus modular design and assembly reveals that a carefully designed modular seat system is not only cost- and time-effective from an assembly and product development aspect, but also crucial for serviceability and early failure mode detection and avoidance. It is concluded that modular seat system design improves engineering efficiency by balancing of functional/attribute requirements, product design, manufacturing, assembly, and supply-chain management.