The article is about homosexual behavior in animal. This behavior consists of various sexual activities such as the copulation of individuals having same sex, mutual masturbation, the common care over the progeny or couple formation. Homosexual behaviors have been documented in different animal groups, such as birds, reptiles, mammals, insects and spiders. The homosexuality among animals could develop under natural selection as an adaptation. For instance it can reduce of the intraspecific aggression, settle of the hierarchy in the group of non-related individual or it can be directly connected with heterosexual reproductive success. Homosexual behavior can also be a result of animal error living in unusual situation, for instance in captivity.