The process of making something immune. It is commonly used both as a medical term and a legal term.

In the medical context, immunization refers the introduction of a vaccine or similar agent for purpose of rendering a body immune to disease. Vaccines introduce a small amount of a virus (often a dead form that cannot spread) into the body, triggering the production of antibodies. The antibodies then provide protection against the real virus. Some common examples are childhood immunization to diphtheria and measles. Some diseases, such as diphtheria and smallpox, have been rendered extremely rare or completely extinct through widespread immunization through vaccination.

In the legal context, immunization refers to being made excempt from the normal legal duties or liabilities. For example, a witness can sometimes be offered immunity in exchange for testifying.