The most common sexual positions are man-on-top, woman-on-top, side-by-side, and rear-entry. Some heterosexual couples and some gay men also practice anal intercourse. They may all be modified by performing them lying down, sitting, standing, kneeling, or any combination of these. Each couple's inventiveness and comfort level determines their choice of positions.

The man-on-top position is the most common of all intercourse positions in Western cultures. It is also called the missionary position after the 19th century Christian missionaries who believed that the man on top was the only natural and proper position for intercourse. They encouraged their foreign converts to abandon their so-called "animal" positions in favor of the man-on-top position. In the man-on-top position the woman lies on her back with her legs spread. Either the man or the woman guides the penis into the vagina. The man can lie flat on the woman if his weight is not uncomfortable on her, or he can support some or all of his weight on his elbows, hands or knees. Some women find that without this, the weight of the man on them restricts their pelvic movements. The woman can wrap her legs around the man's hips or back, or even put them up over his shoulders. The further up her legs are the deeper the penetration the man can make as he thrusts. Some women, however, do not care for the deep penetration this position encourages.

The man-on-top position somewhat limits the ways a man can use his hands to caress his partner, but the woman can use her hands freely to caress the man or stimulate her clitoris. It is a very good position for seeing each other and kissing during intercourse.

For the woman-on-top position, the man lies on his back and the woman lowers herself onto his erect penis. Either the man or the woman may guide the penis into the vagina. The woman can remain squatting on her knees facing the man, she can straighten her legs, or she can turn around and face her partner's feet. Couples may also arrive at this position by rolling over from a man-on-top or side-by-side position. On top the woman can regulate the depth of penetration of the penis and the rate of thrusting.

This position also allows for maximal indirect stimulation of the clitoris by the penis, and some women reach orgasm more easily when they are on top than when they are underneath the man. Couples may like this position because they both can move their hands more freely to caress each other than in most other positions. They can also see more of each other. Some women find that penetration is too deep in this position, but they can regulate the depth by limiting how far down they lower themselves. Also, with vigorous movements the penis may slip out of the vagina, which may be frustrating.

The woman-on-top position is less often recommended if the woman is trying to become pregnant because the man's semen naturally tends to run out of her vagina. Of course, women who prefer this position can simply change positions immediately after her partner has ejaculated. Moreover, this is a good position for the later months of pregnancy because it allows intercourse without the woman's growing belly getting in the way. For the same reason it is a good position for men with large stomachs.

The side-by-side position is a position in which the partners have intercourse lying on their sides facing each other. A couple can start off in this position or arrive at it by rolling over from man or woman on top. Deep pelvic thrusting is difficult when a couple is side by side and some couples prefer not to use the position for that reason. On the other hand, both partners' hands are free to caress each other and the face to face position allows them to kiss. Because energetic thrusting is difficult when side by side, this is a particularly good position for people who need to avoid strenuous activity. It is also a useful position during pregnancy because the woman's belly gets in the way less than, for example, in the man-on-top position.

Rear entry intercourse is when the man's penis enters the woman's vagina when she has her back to him. It is not the same as anal intercourse, which is intercourse with a man's penis inserted in his partner's rectum. Rear entry intercourse can be done with the woman standing but bending over and supporting herself, or with the woman on her hands and knees and the man kneeling behind her (commonly known as doggy style). Or rear entry can be done with both partners lying on their sides, her back to his front.

Rear entry allows for deep penetration and vigorous pushing if the couple wants that. The man's hands are free to caress the woman and he can reach her clitoris easily. It is more difficult for the woman to caress the man in this position than in others because she has to reach behind her. The drawbacks of rear entry intercourse are that the penis entering from behind gives very little stimulation to the clitoris and some couples do not like the lack of face-to-face intimacy.

Which sexual positions a couple uses depends on a variety of factors. Each partner's physical comfort with a position certainly influences its use, as might their inhibitions about experimenting with unfamiliar positions. Sometimes the capacity to prolong or hasten orgasmic response determines what position a couple may choose. In some cases, circumstances (e.g. amount of space or time available) dictate the position for intercourse. Some couples will use one position almost to the exclusion of all others, perhaps because they mutually find it to be the most satisfying. Other couples may regularly use several positions or experiment with positions but not regularly include them in their lovemaking. Whatever the choices made, couples may find that the position influences the emotional as well as the physical aspects of lovemaking.

With the exception of coitus, sexual positions for gay and lesbian couples do not differ much from those of heterosexual couples. Gay men may engage in anal intercourse more often than heterosexual couples and gay women may be more likely to introduce sex toys into their lovemaking. However, the vast array of sexual positions that same or opposite sex couples may experience remains basically the same.