The authors of this Comment—a lawyer and a physician—suggest that most physicians who are called upon to testify concerning medical issues in personal injury litigation do not understand that judges and attorneys view “causation” quite differently than do members of the medical community. For example, medical practitioners tend to be concerned with all possible causes of the patient's current medical condition, whereas legal practitioners in personal injury cases generally focus on a particular event as possibly precipitating, hastening, or aggravating a particular aspect of the patient's condition to the extent that the event in question is, in legal language, the “proximate cause” of an injurious result. The authors summarize and analyze the differences—and the occasional similarities—between the medical and the legal approaches to causation, in the hope that they will thereby (1) contribute to greater understanding by the two professions of each other's theory and practice, and (2) help the expert medical witness to be more comfortable and more effective in his courtroom role.