E-mail has the potential to improve both the quality and efficiency of healthcare service delivery. Despite the substantial growth of this form of communication over the past decade, its promise to patients, providers, and their health plans remains largely untapped. In this article we (1) review the literature on e-mail use between patients and providers; (2) identify challenges and opportunities facing managed care organizations that wish to maximize the potential of this form of communication; (3) describe the components of 2 systems aimed at enhancing e-mail use in clinical settings; and (4) discuss the implications of increased e-mail use for managed care.