An oviparous animal is one that reproduces by laying eggs. In oviparity, fertilization of the female ova (eggs) occurs inside the body, but once achieved the eggs are laid and subsequently hatch outside her body. Unlike viviparity, the developing embryo receives all its nutrition from the egg. Oviparity is the most common form of reproduction and occurs in all animals except marsupials and placental mammals.

In ovoviparity, a female's fertilized ova develop and hatch inside her oviducts. Unlike viviparity, during oviviparity development the zygotes receive no nutrition from the mother as no placenta is present. Ovoviparity is common in many invertebrate animals and some fish and snakes. When the young emerge, the mother appears to be giving birth to live young, although they have only just hatched.