This chapter discusses design-decision support in concurrent/simultaneous engineering.It presents three different approaches to process planning and the involved difficulties. Resulting from the perspective of process planning, the chapter focuses on the key aspect design for economic manufacturability with emphasis on design-decision supporting activities. Classical and knowledge-based design-decision support tools are introduced and discussed. C/S engineering emphasizes people and communication issues rather than technology issues. The basic idea is based on a fundamentally different way of looking at how products are conceived, engineered, manufactured, and supported. Interactive communication among the different disciplines involved in the development process provides the necessary process insight for the members of the management, the technical staff, and the labor. Product design is generally concerned with form, fit, and function. Manufacturing aspects, quality assurance, and arising costs are often not considered until later stages of product development, so that designs need to be reworked to solve occurring problems or failures.