Theories and practices in early childhood education continually evolve, and the same is true in the health field. Such change is especially apparent in the area of childhood immunizations. Since vaccination to prevent smallpox was first started in the late 1700s, recommendations for which immunizations to give and when to give them have been revised frequently. Early childhood programs are in a unique position to educate and assist families regarding this effective method of preventing serious illnesses. Fortunately, much information and many tools are available to support early childhood professionals in this important public health effort. In this article, the author discusses how vaccines work and why children have to be immunized. Some of the immunizations typically required for children to attend early childhood programs and a brief description of the diseases they prevent are provided. (Contains 7 online resources.)