Autoimmunity is a normal event, while autoimmune diseases result from an aberration of this normal phenomenon. The etiology of this switch is considered multifactorial with the final common pathway being the loss of normal self-tolerance in a particular organ or group of organs. Genetic, environmental, hormonal and immunologic factors (along with probably other yet unrecognised factors) are considered important in the development of these disorders. The particular autoimmune disease which any patient develops is most likely a result of which combination of factors the patient has accumulated. We begin with a brief review of immunobiology in order to arrive at a suitable definition of autoimmunity. This is followed by a concise description of the current theories regarding the development of autoimmune disease and the factors known to be associated with these illnesses. Concluding remarks address the factors that normally prevent the progression of autoimmunity to autoimmune disease and the application of current knowledge to future therapeutic approaches.