Today’s business environment and the increasing complexity of products has led to a shift away from traditional ways of innovating (i.e., in-house) towards involving partners in the product and technology development process. Despite the predicted positive outcomes for interorganizational collaborations, such as decreased costs and higher product quality, these projects often fail or fall short of expectations. Several studies have investigated the link between involving external partners in new product development (NPD) projects and performance, but mixed results demonstrate that managing such projects remains a challenge. In a meta-analytical effort, this study synthesizes extant empirical to identify performance-related antecedents of interorganizational NPD projects. After a thorough search of literature, twelve potential antecedents were identified and nine (environmental uncertainty, project duration, integration, clarity of goals and roles, partner’s knowledge and competence, complementarity, communication and collaboration, trust and conflicts) out of these twelve antecedents were significantly related to project performance. In contrast, product and technology newness, formalization, and partner experience did not show a significant relationship with NPD project performance. Moderator analyses showed that relationships differ depending on the indicator (project efficiency or product outcome) used to measure the performance of the NPD project.