There is a growing emphasis on the importance of collaborative science. Evaluating efforts to increase collaboration among researchers, however, is a challenge. We will describe the evaluation of the AHRQ Multiple Chronic Conditions Research Network, a project aimed at accelerating a new field of research by encouraging and facilitating information sharing and collaboration across independently funded investigators. We will present the main challenges we faced evaluating this effort, and discuss lessons learned. For example, while we collected both quantitative and qualitative data for this evaluation, we found the qualitative results to be more useful mainly because definitions of “collaboration” varied across participants and most results were subtle. Finally, we will share a framework of collaboration that we believe could be adapted to help future evaluators define and measure varying levels of collaboration among research investigators. #2013Conference #GovernmentEvaluation