Together with the University of Antwerp Vaccine & Infectious Disease Institute and the Centre for Health Economics Research and Modelling Infectious Diseases, Project Tycho organized a workshop in Antwerp about a systematic approach to estimating the historical impact of childhood immunization in European countries. This workshop was supported by independent grants from Sanofi Pasteur and GlaxoSmithKline. During this 2-day workshop on February 22-23, 30 researchers and representatives from immunization programs in England, France, Germany, Italy, Spain, Belgium, The Netherlands, Denmark, Slovak Republic, and Chech Republic discussed opportunities to quanitfy the historical impact of immunization programs in Europe. For most countries, historical data that have already been collected on the incidence of disease could be used for vaccine impact studies. Historical data is not always easily available and will likely need digitization, curation, and standardization before they can be used for research. The Project Tycho team shared their experience with data digitization and curation for the United States and is looking forward to new partnerships in Europe for similar work.