This study investigates the relationship between the number of partners in cooperative new product development and the scope of the development project, the projected market size for the product, and the likelihood the product will be launched. With drug development in the pharmaceutical industry as the setting, the hypotheses are tested using hierarchical modeling and a dataset of 7,167 drugs across 86 firms during the period 1995 – 2006. Results suggest that the number of development partners is positively related to the scope of knowledge categories underlying the development effort, while the scope of product applications is associated with market size.