A male factor plays a role in half of infertility cases. The causes are summarised in this review, and they include hormonal disturbances, genetic alterations, testicular disease, obstruction, and ejaculatory dysfunction. Evaluation may reveal a correctable cause or uncover underlying disease. In a few cases of pretesticular infertility, medical treatment may have effect, and in cases of obstruction or varicoceles, surgical treatment may correct the problem. In cases with ejaculatory dysfunction, assisted ejaculation often produce viable sperm. Sperm for assisted reproduction may also be obtained by aspiration or surgery.