The classification of breast tumors and differentiation of stages in men, as well as in women, is necessary for defining tactics, methods of treatment, duration of therapy, volume of surgery, follow-up strategy, and prognosis. Male breast cancer is not separately classified as an independent nosology. Existing classifications accepted for breast carcinoma in women are most often used. Some classifications of breast cancer are based on clinical and etiological features, imaging methods, and pathology to characterize the primary breast tumor, its spreading, and local and remote metastases. Some examples of clinical classifications that have been used in different countries are those proposed by Holdin in Russia and the countries of former USSR, by Holsted and Manchester in Great Britain, by Colombian in the United States, and by Steinthal in European countries. The international clinical classification based on the TNM system is now the most appropriate for breast cancer staging. © Springer International Publishing Switzerland 2015.