A cock ring or cockring is a ring that is placed around a man's penis, usually at the base, primarily to slow the flow of blood from the erect penile tissue, thus maintaining erection for a longer period of time. Cock rings can be worn around just the penis or penis and scrotum, or just the scrotum alone, though this is usually designated as a testicle cuff. Rings can be made of a variety of different materials, most commonly leather, rubber, or silicone, though nylon and metal are also used either as the main component or part of the closure. The term cock ring is sometimes used as a synonym for a Prince Albert piercing, a piercing of the penis that is usually, though not always, a metal ring.

A man may wear a cock ring because he has erectile dysfunction (ED), erectile hyperfunction, or otherwise wants to prolong erection because he likes the particular sensation of tightness and extreme engorgement that wearing one provides. It can be worn as a sex toy, as jewelry, or simply for the appearance. When used for ED, a vacuum pump is used to produce an erection in spite of vascular or nerve damage, and the ring slid off the pump's cylinder onto the base of the penis to maintain the erection.

Some men enjoy using cock rings for masturbation, as wearing of this sex toy contributes to better erection and delays orgasm, thus it intensifies orgasmic sensations. Also vibrating cock rings deliver a great range of very pleasurable vibrations that enhance enjoyment.