Vaccines are crucial to maintaining public health. They are a safe, cost-effective, and efficient way to prevent sickness and death from infectious diseases. Vaccines have led to some of the greatest public health triumphs ever, including the eradication of naturally occurring smallpox from the globe and the near eradication of polio. The immune system is a network of cells, tissues, and organs that work together to defend the body against attacks by foreign invaders. These are primarily microbes; tiny organisms such as bacteria, parasites, and fungi that can cause infections, but are too primitive to be classified as living organisms. This book provides an overview about vaccines and the immune system, including how vaccines and the immune system work and prevent disease, how vaccines are made and what vaccine research might achieve in the future.