Defining and measuring patient safety is an ongoing challenge. This systematic review explored international approaches to defining serious reportable patient safety incidents. Findings indicate wide variation in terminology and reporting systems among countries which may contribute to missed opportunities for learning. Serious reportable patient safety events were commonly defined as being largely preventable; having the potential for significant learning; causing serious harm or having the potential to cause serious harm; measurable and feasible to report, and; running the risk of recurrence.