Autoimmunity (also called autoallergy) is an immune response against animals's own Ags; that is to say, "An endogenous immune response to an endogenous Ag". It indicates a failure of immunological tolerance body's own Ags. The state of autoimmunity has been unequivocally demonstrated both in man and in experimental animals and is the pathogenic mechanisms in certain diseases. This book presents various autoimmune disorders affecting the oral cavity.