Abstract. This paper compares organization and practices for software reuse in integrationoriented software product lines and open source software projects. The main observation is that both approaches are successful regarding large variability and reuse, but differ widely in practices and organization. To capture practices in large open source projects, we describe an open compositional model, which reflects their more decentralized organization of software development. We capture key practices and organizational forms for this and validate these by comparing four case studies to this model. Two of these studies are based on published software product line case studies, for the other two we analyze the practices in two large and successful open source projects based on their published developer documentation. Our analysis highlights key differences between the practices in the two open source organizations and the more integrational practices used in the other two cases. Finally, we d...