The Division of Services and Intervention Research of the National Institute of Mental Health (NIMH) utilizes a variety of methodologies and approaches in the development of its clinical trials program. In this article, we describe the need for large multisite trials; the mechanisms for addressing this need; and the various approaches that have been used. In the course of carrying out this initiative, we have created opportunities for the Institute and its trial investigators to receive advice and input from the field. We describe the role and function of the trial coordinating center and NIMH staff. We identify the first steps to be taken in the initiation of a trial and highlight the opportunity for ancillary studies. Finally, we enumerate some of the pitfalls of large clinical trials and discuss measures taken to anticipate and address them.