Medical education during the past decade has witnessed a significant increase in the use of simulation technology for teaching and assessment. Contributing factors include: changes in health care delivery and academic environments that limit patient availability as educational opportunities; worldwide attention focused on the problem of medical errors and the need to improve patient safety; and the paradigm shift to outcomes-based education with its requirements for assessment and demonstration of competence. The use of simulators addresses many of these issues: they can be readily available at any time and can reproduce a wide variety of clinical conditions on demand. In lieu of the customary (and arguably unethical) system, whereby novices carry out the practice required to master various techniques--including invasive procedures--on real patients, simulation-based education allows trainees to hone their skills in a risk-free environment. Evaluators can also use simulators for reliable assessments of competence in multiple domains. For those readers less familiar with medical simulators, this article aims to provide a brief overview of these educational innovations and their uses; for decision makers in medical education, we hope to broaden awareness of the significant potential of these new technologies for improving physician training and assessment, with a resultant positive impact on patient safety and health care outcomes.