The product platform development process becomes critical and of general interest when different brand name products are developed from inter-firm developed product platforms. The inter-firm platform adds perspectives not considered in previous research. In this article areas related to the inter-firm product platform integration process are described. The study is a longitudinal, deep, explorative study aimed at identifying managerial challenges to inter-firm platform development and how they can be dealt with. Analysis shows that the factory sequence is a critical factor when developing inter-firm platform architecture. Also, making architectural concessions without jeopardising brand uniqueness places new demands on managers involved in the development processes. Further, we found a reciprocal interdependence between technological and managerial factors that created a need for innovative organisational and managerial solutions. Finally, reciprocal interdependences add complementary theoretical knowledge on how to better control and understand areas that hamper inter-firm product development projects from attaining cost-effective solutions and economies of scale.