This topical area covers the body’s non-specific defences against diseases and includes physical and chemical barriers. The body’s immune system covers specific immune responses such as the modes of action of phagocytes and lymphocytes; summarising the actions of B and T lymphocytes in fighting infection. Memory cells take part in establishing long-term immunity and this unit goes some way in explaining this and further more the molecular structure of antibodies to their function. Active passive natural and artificially-acquired immunity are discussed in detail and an understanding of how vaccination may control disease is discussed and ultimately how vaccines are produced. From this information, the effectiveness of different vaccines can be discussed: i.e vaccine for small pox and programmes aimed at controlling diseases such as measles, polio,TB, influenza, malaria or cholera. Further discussion is made on the current developments in clinical and medical application in relation to areas such as transplant surgery, allergies, auto–immune disease and other relevant fields.