Gynecomastia is a common finding that is present in up to 57% of men. It is caused by proliferation of the mammary glands, which leads to the development of dense subareolar tissue. The condition results from both physiologic (eg, hypogonadism, altered estrogen-to-androgen ratio) and nonphysiologic (eg, drugs, herbal products) causes. Most cases are benign and resolve spontaneously. Treatment is usually unnecessary, although there are specific signs and symptoms that warrant further workup. Psychosocial effects also are of concern, particularly among adolescents. Knowledge of the possible causes of gynecomastia and a thoughtful approach to the patient presenting with this condition can lead to improved outcomes and patient satisfaction. This concise review of the common presentation, etiologies, diagnosis, and treatment of gynecomastia should aid healthcare professionals who may encounter these patients in their practices.