The Cochrane Collaboration has established a centralized database of controlled trials and other studies of health care interventions (called CENTRAL) that serves as the best available resource for all those preparing and maintaining systematic reviews or otherwise searching for trials. CENTRAL is available on The Cochrane Library. This article describes the history and methods of CENTRAL's development and the results of an analysis of the current composition of CENTRAL. As of September 2000, CENTRAL contained almost 300,000 citations to reports of trials, contributed mainly by Cochrane Groups and Centers around the world. Development of CENTRAL has been an ambitious, scholarly undertaking and has resulted in a valuable resource: CENTRAL includes citations to controlled trials that may not be indexed in MEDLINE, EMBASE, or other bibliographic databases; citations published internationally in many languages; and citations that are available only in conference proceedings or other hard-to-access sources.