In this survey, we review published investigations and trials of vaccines among twins. We identified 29 original studies, dating back to 1979. The studies include determinations of the role of genetics and environment in the variation in immune response to vaccination, the investigation of adverse events in which vaccination was the suspected etiologic agent, and the occurrence of vaccine preventable diseases or their complications. Specific methods include case reports, cross-sectional surveys, prospective surveys, and double-blind, randomized, placebo-controlled, cross-over studies. We examine three of these studies in detail to illustrate important opportunities and limitations of twins studies in vaccinology.