PURPOSE: Medicare's merit-based incentive payment system and narrowing of physician networks by health insurers will stoke clinicians' and policy makers' interest in care delivery attributes associated with value as defined by payers. METHODS: To help define these attributes, we analyzed 2009 to 2011 commercial health insurance claims data for more than 40 million preferred provider organization patients attributed to over 53,000 primary care practice sites. We identified sites ranking favorably on both quality and low total annual per capita health care spending ("high-value") and sites ranking near the median ("average-value"). Sites were selected for qualitative assessment from 64 high-value sites and 102 average-value sites with more than 1 primary care physician who delivered adult primary care and provided services to enough enrollees to permit meaningful spending and quality ranking. Purposeful sampling ensured regional diversity. Physicians experienced in primary care assessment and blinded to site rankings visited 12 high-value sites and 4 average-value sites to identify tangible attributes of care delivery that could plausibly explain a high ranking on value. RESULTS: Thirteen attributes of care delivery distinguished sites in the high-value cohort. Six attributes attained statistical significance: decision support for evidence-based medicine, risk-stratified care management, careful selection of specialists, coordination of care, standing orders and protocols, and balanced physician compensation. CONCLUSIONS: Awareness of care delivery attributes that distinguish their high-value peers may help physicians respond successfully to incentives from Medicare and private payers to lower annual health care spending and improve quality of care.