This report from the Council for International Organizations of Medical Sciences (CIOMS) in collaboration with WHO covers the activities and outputs of the CIOMS/WHO Working Group on Vaccine Pharmacovigilance (2005-2010). This working group brought together experts from both industrialized and emerging countries representing regulatory agencies, vaccine industry, national and international public health bodies including WHO and CIOMS, academia and clinical care, contributing from their different perspectives. The report covers general terms and definitions for vaccine safety and discusses the application of such harmonized tools in vaccine safety surveillance and studies. As well, the report highlights case definitions for adverse events typically reported for vaccines. The report is addressed to those engaged in vaccine safety data collection and evaluation, and will also make a useful reading for others who want to familiarize themselves with vaccine safety terminology.