E-mail is now a primary method of correspondence in health care, and proficiency with professional e-mail use is a vital skill for physicians. Fundamentals of e-mail courtesy can be derived from lay literature, but there is a dearth of scientific literature that addresses the use of e-mail between physicians. E-mail communication between providers is generally more familiar and casual than other professional interactions, which can promote unprofessional behavior or misunderstanding. Not only e-mail content but also wording, format, and tone may influence clinical recommendations and perceptions of the e-mail sender. In addition, there are serious legal and ethical implications when unprofessional or unsecured e-mails related to patient-identifying information are exchanged or included within an electronic medical record. The authors believe that the appropriate use of e-mail is a vital skill for physicians, with serious legal and ethical ramifications and the potential to affect professional development and patient care. In this article, the authors analyze a comprehensive literature search, explore several facets of e-mail use between physicians, and offer specific recommendations for professional e-mail use.