Major depression is common, debilitating, underrecognized, and undertreated. Most individuals who do get treatment are cared for solely in primary care settings. Clinical practice guidelines for depression, in combination with team-based quality improvement (QI) for implementing them, offer a potentially valuable tool for improving clinical care and health outcomes for depressed patients. The main purpose of this study is to determine whether team-based quality improvement approaches are more effective than guideline distribution alone for increasing adherence to guidelines for primary care patients with major depression. As a secondary purpose, we will assess two common variants of team-based QI. One of the team-based QI models is more centrally-managed, while the other is more locally managed. We will thus learn about how, whether, and why team-based QI works. We propose a randomized clinical trial in 9 group-practice sites comparing the central expert (CE) form of QI and the local peer (LP) form of QI to distribution alone as methods for implementing the recently-published Agency for Health Care Policy and Research clinical practice guidelines for depression in primary care. We will evaluate the two QI models in 6 sites (4 autonomous practices within Kaiser Permanente of Northern California and 2 firm (team) practices at the Sepulveda VA Medical Center) against a control condition--guideline distribution--in 3 sites (2 Kaiser and 1 Sepulveda VA practice). The QI approaches will be implemented over a 10 month period. To evaluate the effectiveness of the QI approaches, we will enroll 750 depressed patients during the post intervention period, distributed across study sites. We will assess patient health status (including severity of depression) and the quality of the process of care for depression for both samples. We will follow these patients for 12 months to determine their health and cost outcomes and their satisfaction with care. We will also assess health and cost outcomes and their satisfaction with care. We will also assess health care provider attitudes and knowledge, as well as any organizational features that affect the success of the interventions. The study will thus generate new knowledge about guidelines implementation for depression, quality improvement methods, and the barriers and resources for depression care in primary care settings.