Anal sex is stimulation of the anus during sexual activity. It can be done in several different ways: manually, orally or by anal intercourse.

Anal sex can be the primary form of sexual activity or it can accompany other types of stimulation. For instance, couples sometimes include manual stimulation of the anus (either lightly rubbing the rim or inserting a finger into the anus) during vaginal intercourse. Others use the tongue in a similar fashion for oral stimulation.

Anal intercourse is the insertion of a man's penis into his partner's rectum. Although anal sex is often thought of as a strictly homosexual activity, many heterosexual couples enjoy it too.

Anal penetration can be pleasurable, but it can also be a source of physical discomfort. The muscle on the outside of the rectum, called the anal sphincter, ordinarily tightens if stimulated, which means that attempts at insertion of the penis, or even a finger, may be uncomfortable even if done slowly and gently. If penetration into the anus is forced, injury is possible. It is helpful to use a lubricant liberally and to relax and gradually dilate the sphincter by gentle manual stimulation before attempting penetration.

Some people clear the rectum with a small disposable enema before anal intercourse. Because the rectum contains infection causing bacteria, anything (fingers, objects, penis) that has had contact with the anus should not subsequently be in contact with the vagina or mouth until it has been thoroughly washed.