Immunology is the scientific study of the body resistance to invasion by other organisms. In a medical sense, immunology deals with the body's system of defense against disease-causing microorganisms and with disorders in that system's functioning.

Immunology is a branch of biology and medicine that covers the study of immune systems in all organisms. Immunology charts, measures, and contextualizes the physiological functioning of the immune system in states of both health and diseases; malfunctions of the immune system in immunological disorders (such as autoimmune diseases, hypersensitivities, immune deficiency, and transplant rejection and the physical, chemical, and physiological characteristics of the components of the immune system.