Becoming a medical home is a radical change, requiring both a new mental model for primary care and the skills and resources to accomplish it. Although numerous reports indicate practice change is feasible--particularly with technical support and either insulation from or alignment with financial incentives--sustained transformation appears difficult. We identified the following critical success factors: leadership, financial resources, personal and organizational relationships, engagement with patients and families, competence in management, improvement methods and coaching, health information technology properly applied, care coordination support, and staff development. Each factor raises researchable questions about what policies can facilitate achieving success so that transformation becomes mainstream rather than the province of the innovative few.