Urinary retention, defined as the inability to void, is a common medical problem. If unidentified and/or untreated, it may become a serious condition that can lead to kidney damage or urosepsis, compromising the patient's life. Acute urinary retention (AUR) is usually easy to identify and to treat as patients usually complain of hypogastric pain and anuria. Proper bladder drainage with urethral or suprapubic catheter is the first line of treatment, with posterior studies to determine the cause of retention. Chronic urinary retention (CUR) is often much more difficult to identify. It is invariably linked to increased post-void residual urine (PVR), but its asymptomatic nature makes it often a hidden condition. There is a wide range of intrinsic and extrinsic, obstructive and non-obstructive causes affecting the lower urinary tract, which can lead to urinary retention. Due to the differences in urinary physiology and in order to simplify diagnosis and management, these are usually studied separately in men and in women. Management consists of a variety of options depending on the cause of retention, including conservative treatment, drug therapy and several forms of surgery. In this review, we make an overview of the main causes of acute and chronic urinary retention in men and women, focusing on the main aspects of diagnosis and management.