Although standardized patients have been employed for formative assessment for over 40 years, their use in high-stakes medical licensure examinations has been a relatively recent phenomenon. As part of the medical licensure process in the United States and Canada, the clinical skills of medical students, medical school graduates, and residents are evaluated in a simulated clinical environment. All of the evaluations attempt to provide the public with some assurance that the person who achieves a passing score has the knowledge and/or requisite skills to provide safe and effective medical services. Although the various standardized patient-based licensure examinations differ somewhat in terms of purpose, content, and scope, they share many commonalities. More important, given the extensive research that was conducted to support these testing initiatives, combined with their success in promoting educational activities and in identifying individuals with clinical skills deficiencies, they provide a framework for validating new simulation modalities and extending simulation-based assessment into other areas.