Vaccines have contributed to global health and have prevented more than 100 million cases of serious communicable diseases in the United States since 1924. Vaccines are complex entities, both in terms of their components and the technology required to produce them. This presentation provides examples of the effect of vaccines on public health, reviews key elements of the host immune system and how vaccines help to protect against disease, and discusses the complex processes and ongoing safety monitoring involved in vaccine development. The presenter also discusses how, despite guidelines for vaccine administration, attaining high vaccination coverage is an ongoing challenge, in part, due to vaccine hesitancy. Vaccine hesitancy is the delayed acceptance or refusal of vaccines despite their availability. The presenter will review various communication strategies to address vaccine hesitancy, enhance communication, and reinforce vaccination needs.