Immunology deals with the study of cells, molecules, and organs that participate in their recognition and processing, as well as how they respond or interact with each other. It also involves the study of the outcomes, desirable or undesirable, and how to suppress or enhance them.

The normal function of the immune system is to defend against infectious agents or molecules recognized as foreign or "non-self" through the activation of mechanisms initially of innate and subsequently of adaptive immunity. Desirable actions of the immune system also include disease prevention through vaccination, as well as the capability of organ transplantation. However, there are also undesirable consequences of immunity, such as reactions to "self" molecules (autoimmunity), immunosuppression, and hypersensitivity reactions.