Theoretical and empirical work on collaboration has proliferated in the last decade. The authors' 2006 article on designing and implementing cross-sector collaborations was a part of, and helped stimulate, this growth. This article reviews the authors' and others' important theoretical frameworks from the last decade, along with key empirical results. Research indicates how complicated and challenging collaboration can be, even though it may be needed now more than ever. The article concludes with a summary of areas in which scholarship offers reasonably settled conclusions and an extensive list of recommendations for future research. The authors favor research that takes a dynamic, multilevel systems view and makes use of both quantitative and qualitative methods, especially using longitudinal comparative case studies.