Exogamy has two related definitions: biological and cultural. Biological exogamy is the mating of non-related beings. Cultural exogamy is the marrying outside of a specific group.

There may be a drive in humans as in many non-human animals to engage in exogamy – out-breeding – because procreating with individuals who are more closely related means any children will be more likely to suffer from genetic defects caused by inbreeding.

The genetic principles involved apply to all species, not just humans. Individuals who breed with more exotic partners and thereby avoid incestuous relationships tend to have healthier offspring due to the benefits of out-breeding. There are many conditions that are more likely where inbreeding takes place, one example being cystic fibrosis when a couple of primarily European genetics have children, another being sickle-cell anaemia when a couple of primarily African genetics have children. Therefore, the drive to reproduce with individuals genetically different from oneself[citation needed] may derive from an innate drive to seek the healthiest combination of DNA possible for one’s offspring by out-breeding. However, that offspring may also imply in losing specific geographic adaptations.

Exogamy is the custom of marrying outside a specified group of people to which a person belongs. In addition to blood relatives, marriage to members of a specific totem, clan(s) or other groups may be forbidden. The opposite of exogamy is endogamy.

Linguistic exogamy is a form of cultural exogamy in which marriage occurs only between speakers of different languages. The custom is common among indigenous groups in the northwest Amazon, such as the Tucano tribes. Also used to describe families in Atlantic Canada with a Francophone and an Anglophone parent.