The concept of the medical home has existed since the 1960s, but has recently become a focus for discussion and innovation in the health care system. The most prominent definitions of the medical home are those presented by the Patient-Centered Primary Care Collaborative, the National Committee for Quality Assurance, and the Commonwealth Fund. These definitions share: adoption of health information technology and decision support systems, modification of clinical practice patterns, and ensuring continuity of care. Each of these components is a complex undertaking, and there is scant evidence to guide assessment of diverse strategies for achieving their integration into a medical home. Without a shared vocabulary and common definitions, policy-makers seeking to encourage the development of medical homes, providers seeking to improve patient care, and payers seeking to develop appropriate systems of reimbursement will face challenges in evaluating and disseminating the medical home model.