The medical home model–an approach to offering excellent primary care–is gaining momentum. A wide range of stakeholders are now embracing medical homes, and the Affordable Care Act has dedicated resources to developing and spreading the model. In this context, states have been leaders in building medical homes – especially for vulnerable populations. Several of the most promising state medical home initiatives have entailed interagency collaboration. This report details best practices and policy considerations for collaborative medical home building in four areas: laying foundations for partnership, and then working together to engage patients and families, engage health care providers and practices, and build strong systems of care.