Mass immunization is the blitzkrieg of vaccination practice. It serves to rapidly protect populations, both because of the high coverage achieved and because of the herd immunity thereby induced. However, as in war, mass immunization campaigns must be conducted intelligently, with careful strategy and strong attention to logistics of supply and deployment. If conducted badly, mass immunization may fail or even be counter-productive. In this volume, some of the most successful practitioners of mass im- nization tell us about its art and science. David Heymann and Bruce Aylward of WHO begin the book with a theoretical and practical overview of mass immunization. Michael Lane, who participated in the successful effort to eradicate smallpox relates how this was done using mass vaccination and other strategies. Application of mass immunization by the US military is c- ered by John Grabenstein and Remington Nevin, who have a large experience in these matters. Karen Noakes and David Salisbury recount the striking s- cesses of mass immunization in the United Kingdom. The global control of the clostridia that produce diphtheria toxin is described by Charles Vitek. Hepa- tis A is decreasing dramatically under the impact of large-scale vaccination, as Francis André illustrates. The French experience with Hepatitis B vac- nation has been mixed, and François Denis and Daniel Levy-Bruhl explain the circumstances. Influenza vaccination is an annual example of large-scale campaigns, the complexity of which is recounted by Benjamin Schwartz and Pascale Wortley.