WHO and the United Nations Children\'s Fund (UNICEF) annually review data on immunization coverage to estimate national coverage with routine service delivery of the following vaccines: bacille Calmette-Gu̩rin/ diphtheria-tetanus-pertussis- first and third doses/ either oral polio vaccine or inactivated polio vaccine- third dose of either/ hepatitis B- third dose/ Haemophilus influenzae type b- third dose/ and a measles virus-containing vaccine- either for measles alone or in the form of a combination vaccine- one dose. The estimates are based on government reports submitted to WHO and UNICEF and are supplemented by survey results from the published and grey literature. Local experts- primarily national immunization system managers and WHO/UNICEF regional and national staff- are consulted for additional information on the performance of specific immunization systems. Estimates are derived through a country-by-country review of available data informed and constrained by a set of heuristics/ no statistical or mathematical models are used. Draft estimates are made- sent to national authorities for review and comment and modified in light of their feedback. While the final estimates may not differ from reported data- they constitute an independent technical assessment by WHO and UNICEF of the performance of national immunization systems. These country-specific estimates- available from 1980 onward- are updated annually.