Abnormal uterine bleeding (AUB) is the term used to describe uterine bleeding that varies from the normal parameters of menstruation. This term replaces several previously used terms with less clear or conflicting definitions, including dysfunctional uterine bleeding, irregular menstrual bleeding, and menorrhagia. PALM-COEIN is a classification system for the etiologies of AUB in nongravid menstruating women. PALM refers to discrete structural entities (ie, polyp, adenomyosis, leiomyoma, malignancy and hyperplasia); COEIN refers to nonstructural etiologies (ie, coagulopathy, ovulatory dysfunction, endometrial, iatrogenic, not yet classified). The prevalence of AUB is estimated to be 35% or higher. The history and physical examination are key in the evaluation of patients with AUB. Patients with symptomatic acute blood loss require urgent evaluation for potential hemodynamic instability. For women 45 years and younger with AUB, endometrial biopsy is indicated if specific risk factors for endometrial cancer are present. Endometrial biopsy is indicated for all patients with AUB who are older than 45 years or have postmenopausal bleeding. Management of AUB is determined by its etiology, and typically consists of medical therapy (ie, combination oral contraceptives, progestin-containing intrauterine devices, tranexamic acid, nonsteroidal anti-inflammatory drugs). Patients with structural lesions may require surgical procedures. Management should be individualized and patient desire for current or future fertility should be considered.