OBJECTIVE: To assess the impacts of the characteristics of quality improvement (QI) teams and their environments on team success in designing and implementing high quality, enduring depression care improvement programs in primary care (PC) practices. STUDY SETTING/DATA SOURCES: Two nonprofit managed care organizations sponsored five QI teams tasked with improving care for depression in large PC practices. Data on characteristics of the teams and their environments is from observer process notes, national expert ratings, administrative data, and interviews. STUDY DESIGN: Comparative formative evaluation of the quality and duration of implementation of the depression improvement programs developed by Central Teams (CTs) emphasizing expert design and Local Teams (LTs) emphasizing participatory local clinician design, and of the effects of additional team and environmental factors on each type of team. Both types of teams depended upon local clinicians for implementation. PRINCIPAL FINDINGS: The CT intervention program designs were more evidence-based than those of LTs. Expert team leadership, support from local practice management, and support from local mental health specialists strongly influenced the development of successful team programs. The CTs and LTs were equally successful when these conditions could be met, but CTs were more successful than LTs in less supportive environments. CONCLUSIONS: The LT approach to QI for depression requires high local support and expertise from primary care and mental health clinicians. The CT approach is more likely to succeed than the LT approach when local practice conditions are not optimal.