Ejaculation is the ejecting of semen from the penis, and is generally accompanied by orgasm. It is the result of sexual stimulation, which may include prostate stimulation. Ejaculation may occur unexpectedly during sleep (a nocturnal emission). The process of ejaculation is an intense sensation, which can be immensely pleasurable and satisfying for males. Each spurt is related with a wave of sexual pleasure, especially in the penis and loins. The first and second convulsions are the most intense in sensation, and produce the greatest quantity of semen. Thereafter, each contraction is linked with a diminishing volume of semen and a milder wave of pleasure. During sexual intercourse, most males will find it difficult to resist the psychological temptation to continue the stimulation of the penis to the point of ejaculation once the feeling of orgasm becomes imminent. During the process, males may make involuntary vocalizations such as grunting, groaning, moaning, or crying out, and some may experience full body convulsions, the spasms in tempo with those in the penis.

Ejaculation generally has two phases: emission and ejaculation proper. The emission phase of the ejaculatory reflex is under control of the sympathetic nervous system, whereas the ejaculatory phase is under control of a spinal reflex at the level of the spinal nerves S2-4 via the pudendal nerve. During emission, the two ducts called as vas deferens contract to propel sperm from the epididymis where it was stored up to the ampullae at the top end of the vas deferens. The beginning of emission is typically experienced as a "point of no return," also called as point of ejaculatory inevitability. The sperm then passes through the ejaculatory ducts and is mixed with fluids from the prostate, seminal vesicles, and the bulbourethral glands to form the semen, or ejaculate. During ejaculation proper, the semen is ejected through the urethra with periodic contractions. These periodic or rhythmic contractions are part of the male orgasm. The typical male orgasm lasts for about 17 seconds but can vary from a few seconds up to about a minute. After the start of orgasm, pulses of semen start to flow from the urethra, reach a peak discharge and then diminish in flow. Typically, orgasm consists of 10 to 15 contractions. The rate of contractions steadily slows during the orgasm. Initial contractions occur at an average interval of 0.6 seconds with an increasing increment of 0.1 second per contraction.

Semen begins to spurt from the penis during the initial or second contraction of orgasm. In general for most men the first spurt occurs during the second contraction. The force and amount of ejaculation vary widely from one male to another. A normal ejaculation contains anywhere from 1.5 to 5 milliliters. The number of sperm in an ejaculation also varies widely, depending on many factors, including the average warmth of the testicles, the recentness of last ejaculation, the degree and length of time of sexual excitement prior to ejaculation, the age, testosterone level, the nutrition and especially hydration and the total volume of seminal fluid. An unusually low sperm count, not the same as low semen volume, is known as oligospermia, and the absence of any sperm from the ejaculate is referred as azoospermia.