Engineered-to-order (ETO) networks are dynamic and hard to define, and their planning and control functionalities are commonly affected by the actions of suppliers and customers. Frequently, projects experience delays, budget overruns, and quality defects. Consequently, there is a need for project management that synchronizes engineering and production processes throughout the network.The aim of this study is to develop a project planning maturity model (MMPP) in order to improve project performance in ETO manufacturing networks. Moreover, a multiple case study approach is used to test the applicability of the developed maturity model. The results of the case studies from three ETO case companies show that there is (1) no or low degree of standardization of the planning processes, and (2) there is little or no integration between engineering and production planning processes.