Ultraviolet (UV) radiation can exert a variety of biological effects, including induction of skin cancer, premature skin ageing and inhibition of the immune system. The immunosuppressive properties of UV radiation are of major biological relevance since suppression of the immune system by UV radiation is not only responsible for the exacerbation of infectious diseases following UV exposure, but also contributes to the induction of skin cancer. Hence, understanding of the mechanisms by which UV radiation compromises the immune system is of primary importance. UV radiation suppresses the immune system in multiple ways. It inhibits antigen presentation, stimulates the release of immunosuppressive cytokines and induces the generation of lymphocytes of the suppressor subtype. In the following, some of the basic mechanisms underlying UV-induced immunosuppression will be discussed.