Recent research highlights significant risks associated with health professionals working long hours—risks to their health and safety, to the safety and quality of care provided to patients, and to public safety. This article undertakes a review of the various instruments used to regulate working hours in health systems, using six countries (Australia, Canada, Denmark, New Zealand, the United Kingdom, and the United States) and the European Union as primary comparators. The review demonstrates differences in the instruments used to regulate the issue in these countries and in the economic, social, and cultural factors that limit instrument choice and moderate instrument effectiveness.