Testosterone deficiency can occur in males of all ages. In adult males, it is induced by endogenous testosterone decline through aging and other modifiable factors. Recent publications suggested the importance of the magnitude of longitudinal decline of testosterone from baseline. The baseline level and the longitudinal decline have individual variability influenced by individual factors including digit ratio, CAG repeat of the androgen receptor and sirtuin activity. Regarding treatment for testosterone deficiency, testosterone replacement therapy is the gold standard for the management of testosterone-deficient patients, and it improves three domains of testosterone deficiency symptoms, such as the physical, psychological and sexual domain. Recent reports suggested the importance of modifiable factors in the testosterone decline in addition to aging. Therefore, it might be responsible for the prevention of testosterone deficiency symptoms to maintain testosterone secretion taking account of the modifiable factors. The present article reviews the literature, and introduces contemporary perspectives and management of testosterone deficiency.