Mating systems correspond to reproductive adaptations to ecological conditions. It is behaviors used by animals to meet compatible mates for sexual reproduction.

Animals use a multiplicity of methods to mate, fusion of sperm and egg, or all of which promote fertilization. Copulation means unions of the sex organs of two sexually reproduce animals for insemination and successive internal fertilization. The two those may be of opposite sexes or hermaphroditic.

Much other kind of animal species reproduces sexually with exterior fertilization, including many basal vertebrates. Some vertebrates imitate with internal fertilization through cloacal copulation, while mammals copulate vaginally.

The ecological behaviors have identified as three divisions of monogamy. They are sexual monogamy in which animals mate with only one partner, habitually for only one mating season and the social monogamy in which a pair mates and raise offspring but either partner might also copulate with others and genetic monogamy in which a female progeny are sired by only one father.

Polygamy is a mating system in which a single creature of one gender has mating contact to several individuals of the opposite gender.

Conceivably the most remarkable fact about animal mating is the size of the sex parts. The verification for the largest testes in the animal kingdom is the northern right whale.