The HMO Research Network (HMORN) is a consortium of 16 health care systems with integrated research centers. Approximately 475 people participated in its 17(th) annual conference, hosted by the Department of Population Medicine, Harvard Pilgrim Health Care Institute and Harvard Medical School. The theme, "Collaborations in Population-Based Health Research," reflected the network's emphasis on collaborative studies both among its members and with external investigators. Plenary talks highlighted the initial phase of the HMORN's work to establish the NIH-HMO Collaboratory, opportunities for public health collaborations, the work of early career investigators, and the state of the network. Platform and poster presentations showcased a broad spectrum of innovative public domain research in areas including disease epidemiology and treatment, health economics, and information technology. Special interest group sessions and ancillary meetings provided venues for informal conversation and structured work among ongoing groups, including networks in cancer, cardiovascular diseases, lung diseases, medical product safety, and mental health.