Background: To advance the science of immunization safety and “vaccinovigilance,” a globally acceptable, common vocabulary for adverse events following immunization (AEFIs) is needed to promote comparability of data. Methods: The Brighton Collaboration develops standardized case definitions and guidelines for data collection, analysis, and presentation via participation of more than 500 experts from 57 countries from public health, clinical care, academia, regulatory organizations, and industry. Results: The first six Brighton case definitions and guidelines have been finalized. Work continues on 17 additional topics. Formal evaluation studies of definitions are underway. More than 67 investigators in 30 countries have begun or are considering implementation of the definitions and guidelines. Conclusions: Standardized and globally implemented case definitions and guidelines for AEFIs will enhance comparability of vaccine safety data and ultimately maintain trust in immunization programs worldwide. The Brighton Collaboration may be a useful model for other realms of patient safety.