Despite the profound and pervasive importance of trust in medical settings, there is no commonly shared understanding of what trust means, and little is known about what difference trust actually makes, what factors affect trust, and how trust relates to other similar attitudes and behaviors. To address this gap in understanding, the emerging theoretical, empirical, and public policy literature on trust in physicians and in medical institutions is reviewed and synthesized. Based on this review and additional research and analysis, a formal definition and conceptual model of trust is presented, with a review of the extent to which this model has been confirmed by empirical studies. This conceptual and empirical understanding has significance for ethics, law, and public policy.