Immunization is the process by which a person is made immune or resistant to an infectious disease, by the administration of a vaccine.

The basic principle of immunization is that the human immune system when attacked by a foreign microbe remembers it specifically and responds against it. So, the next time the microbe or its related organism attacks the body it is being resisted with greater vigour. Using this property vaccines are developed to mimic the original disease causing organism against which vaccination is to be done. This will not result in disease but will prepare the body to fight against the actual pathogen.