William Masters and Virginia Johnson conducted an important program of research on the physiology of human sexual response. They found that two basic physiological processes occur during arousal and orgasm: vasocongestion and myotonia. The sexual response cycle occurs in three stages: excitement, orgasm, and resolution.

Their research indicates that there is no physiological distinction between clitoral and vaginal orgasms in women, which refutes an early idea of Freud's. They also provided convincing evidence of the existence of multiple orgasm in women.

Criticisms of Masters and Johnson's model are that (1) they ignored cognitive factors and (2) their selection of research participants may have led to a self-fulfilling prophecy in their results.

Two cognitive–physiological models are Kaplan's three-component model, focusing on desire, vasocongestion, and muscular contraction, and Walen and Roth's model, which emphasizes cognitive aspects of sexual response, namely perception and evaluation.

The nervous system and sex hormones are important in sexual response. The nervous system functions in sexual response by a combination, of spinal reflexes (best documented for erection and ejaculation) and brain influences (particularly of the limbic system). There is evidence that some women ejaculate. Hormones are important to sexual behavior, both in their influences on prenatal development (organizing effects) and in their stimulating influence on adult sexual behavior (activating effects). Testosterone seems to be crucial for maintaining sexual desire in both men and women.

Pheromones are biochemicals secreted outside the body that play an important role in sexual communication and attraction. Much of the evidence is based on research with animals, but evidence in humans is accumulating rapidly.

Sexual pleasure is produced by stimulation of various areas of the body called erogenous zones.

Sexual self-stimulation, or autoeroticism, includes masturbation and sexual fantasies. Many people have sexual fantasies while masturbating. Common themes of these fantasies are kissing and touching sensuously, oral sex, and seduction. Similar sexual fantasies are also common during intercourse.

An important technique in two-person sex is hand stimulation of the partner's genitals. A good guide to technique is to find out how the partner masturbates. Touching other areas of the body and kissing are also important. The other senses—sight, smell, and hearing—can also be used in creating sexual arousal.

While there are infinite varieties in the positions for intercourse, there are four basic positions: man on top (the missionary position), woman on top, rear entry, and side to side.

The two kinds of mouth–genital stimulation are cunnilingus (mouth stimulation of the female genitals) and fellatio (mouth stimulation of the male genitals). Both are engaged in frequently and are considered pleasurable by many people. Lesbians and gays use techniques similar to those of straights (e.g., hand–genital stimulation and oral– genital sex). Gays and lesbians, though, seem less goal oriented, take more time, and communicate more than heterosexuals do.

Anal intercourse involves inserting the penis into the rectum. This activity and the insertion of other objects in the anus must be done carefully to avoid injury or transmission of STIs.

An aphrodisiac is a substance that arouses sexual desire. There is no known reliable aphrodisiac, and some of the substances that are popularly thought to act as aphrodisiacs can be dangerous to a person's health.

We have a tendency in our culture, perhaps a legacy of the Protestant ethic, to view sex as work and to turn sex into an achievement situation, as witnessed by expressions such as "achieving orgasm." Such attitudes make sex less pleasurable and may set the stage for sexual failures or sexual disorders.