Influenza virus causes annual epidemics and occasional pandemics. Frequent mutations in circulating influenza strains ("antigenic drift") result in the need for annual vaccination. More than two-thirds of persons in the U.S. are recommended for annual vaccination. Because influenza vaccine is available seasonally, mass vaccination strategies are well suited to its delivery. Although doctors offices are the most frequent setting for influenza vaccination overall, workplaces, clinics, and community sites (retail stores and pharmacies) also are common vaccination settings. Influenza vaccination also is delivered in mass vaccination clinics to health care workers and military personnel. Universal influenza vaccination, which has been recommended as a strategy to improve prevention by increasing vaccination coverage and providing indirect protection of adults by decreasing infection and transmission among children, would require expanded use of mass vaccination, for example in schools, as well as in the community. Influenza pandemics occur when a new influenza A subtype is introduced into the population ("antigenic shift"). Most or all of the population is susceptible to the pandemic virus and two doses of vaccine may be needed for protection. U.S. pandemic preparedness and response plans indicate that the entire population should be vaccinated beginning with defined priority groups including those who provide essential services including healthcare and those at highest risk of severe illness and death. Pandemic influenza vaccination will occur primarily through the public sector in mass clinic settings. Vaccination program planning must consider issues including coordination, staffing, clinic location and lay-out, security, record keeping, and communications. Exercising vaccination clinics is important for preparedness and can be done in the context of annual influenza vaccination.