This chapter examines the evolution of vaccination, initially focused on children, and the growing need for adult immunization. It highlights the success of the Expanded Programme on Immunization (EPI) since 1974 in reducing vaccine-preventable diseases globally. As populations age, particularly in Europe, adult immunization has become increasingly critical, especially for older adults and those with chronic diseases. The chapter discusses the impact of demographic shifts, with a rising elderly population, on healthcare systems. It emphasizes the importance of lifelong immunization and the challenges in achieving high vaccination coverage for adults. Various vaccines, including influenza, pneumococcal, and herpes zoster, are identified as essential for adults. The chapter also explores barriers to adult vaccination and strategies to overcome them.