This book addresses various aspects of testicular autoimmunity. It has long been suspected that testicular autoimmunity could be one of the causes of idiopathic male infertility. However, it is very difficult to estimate the incidence of testicular autoimmunity in men, as most male patients first realize they are infertile when they start trying to conceive a child, and there is a possibility that their testes may already exhibit the end stage of testicular autoimmunity, in which lymphocytic inflammation and immunoglobulin deposition in their testes subsided long ago and only the spermatogenic disorder remains. Therefore, autopsy or biopsy for testicular tissues in men before the end stage of testicular autoimmunity and investigations using testicular autoimmunity model animals are needed to determine the epidemiology of testicular autoimmunity.