Tournament species in zoology are those species in which members of one sex (usually males) compete in order to mate. In tournament species, most members of the competing sex never win the competitions and never mate, but almost all members of the other sex do mate with the small group of winners.

Since in the vast majority of tournament species the males compete, the competing sex will be referred to as "the males". Tournament species are characterized by fierce male-to-male competition; males which are significantly larger (up to three times the mass of the female) or possess more natural weaponry or are more gaudily decorated than females; by high variability in male reproductive success, as winning males mate with many females and losing males mate with few or none or die in the competition itself; and by high promiscuity in both sexes, which occasions small or no male parental investment.

In some species, the competition between males involves displays in which females choose winning males; these contests are called leks. In other species, competition is more direct, in the form of fighting between males.

Examples of tournament species include peacocks, in which the female peahens judge male peacocks on the size and coloration of their large and gaudy tail, several species of antelope, in which males use their antlers to fight one another, and Elephant seals, the males of which use their large size to fight one another.

In a small number of species, females compete for males; these include species of Jacana, species of Phalarope, and the spotted hyena. In all these cases, the female of the species shows stereotypically "male" traits: larger bodies, aggressiveness, or even maintenance of a multiple-male "harem".

Most species fall on a continuum between tournament species and pair-bonding species.