In this paper, we first provide a simple framework for cooperation in product development between competitors. We put forward the tradeoff between the benefits obtained through development cost sharing and the cost of intensified competition due to reduced product differentiation, which implies that no cooperation can be an equilibrium outcome. We allow for firms to cooperate partially, i.e., to develop some product components jointly, but not necessarily all components. This enables us to study the factors that may have an effect on the degree of cooperation in product development, both in the presence and in the absence of process R&D. We also analyze the interaction between cooperation decisions on product development and process R&D. By considering a direct link between the two, we show that the degree of cooperation in product development may adversely affect the intensity of cooperation in process R&D.Keywords: Cooperation, Product Development, Process R&D.JEL Codes: L1, O3. * We appreciate the comments of the participants at the 2007 EARIE Conference (Valencia, Spain) and the 2007 Journées de Microéconomie Appliquée (Fribourg, Switzerland). We are grateful to two anonymous referees for very useful remarks and suggestions. We also thank Katie Naeve for her editorial assistance.