A cock ring is a ring worn around the penis, usually at the base. The primary purpose of wearing a cock ring is to restrict the flow of blood from the erect penis to produce a stronger erection. It can also be used to increase girth and/or to maintain an erection for a longer period of time. They are sometimes used as medical devices, on their own or in conjunction with a penis pump to assist in the management of erectile dysfunction. Genital adornment is another purpose, as is repositioning the genitals to provide an enhanced appearance.

When used in cases of erectile dysfunction (ED), they are known by various other names, such as erection rings and tension rings.

Cock rings worn just behind the corona of the glans of the penis are known as glans rings, head rings or cock crowns. A ring that is worn around the penis and scrotum is also usually called a cock ring, but is sometimes referred to as a cock and ball ring. Rings that are worn just around the scrotum, in order to hold the testicles, are called testicle cuffs or ball stretchers.