This chapter provides an overview of immunization and vaccine development, emphasizing the importance of immunology in advancing vaccine science. It highlights the significant impact of vaccines on public health, particularly in reducing childhood mortality. The chapter discusses the history of vaccination, the principles of vaccine design, and the role of immunology in understanding protective immunity. It also addresses the challenges in developing vaccines for difficult-to-target pathogens and the need for improved understanding of immune responses in older adults. The text covers various types of vaccines, including live attenuated, inactivated, and subunit vaccines, and discusses the use of adjuvants to enhance immune responses. Additionally, it explores the concept of immune memory and its implications for vaccine-induced protection, as well as the importance of herd immunity in controlling infectious diseases. The chapter concludes by discussing factors that affect vaccine protection and the need for continued research to improve vaccine efficacy and accessibility.This chapter provides an overview of immunization and vaccine development, emphasizing the importance of immunology in advancing vaccine science. It highlights the significant impact of vaccines on public health, particularly in reducing childhood mortality. The chapter discusses the history of vaccination, the principles of vaccine design, and the role of immunology in understanding protective immunity. It also addresses the challenges in developing vaccines for difficult-to-target pathogens and the need for improved understanding of immune responses in older adults. The text covers various types of vaccines, including live attenuated, inactivated, and subunit vaccines, and discusses the use of adjuvants to enhance immune responses. Additionally, it explores the concept of immune memory and its implications for vaccine-induced protection, as well as the importance of herd immunity in controlling infectious diseases. The chapter concludes by discussing factors that affect vaccine protection and the need for continued research to improve vaccine efficacy and accessibility.