The testes (plural) are the most essential organs of the male reproductive system. They are the glands where sperm and testosterone are produced.

The testes are contained in the scrotum and are composed of dense connective tissue containing around three hundred internal compartments called lobules. Each of these lobules contains a number of coiled, tiny tubules where the sperm are produced. Testosterone is produced in cells located in between the lobules.

Sperm travels through the testis from the tubules, through a network of ducts called the rete testis, to the epididymis.

One of the most common complications that can occur with the testes is an undescended testis, which typically occurs in about two to four percent of all male infants and around thirty percent of boys born prematurely. This occurs when the testes, which form in the abdomen, fail to descend into the scrotum when puberty begins. This can be addressed by either waiting around three to six months after the initial examination for the testis to descend, or with a surgical procedure called an Orchidopexy, which involves artificially moving the testis to the scrotum. The procedure has a 95 percent success rate.