Tetrapods (Greek τετραποδηδόν tetrӑpodēdón, "on all fours"); (Greek τετραπόδηs tetrӑpódēs, correspondent to Latin quadruped, "four-footed") are vertebrate animals having four limbs. Amphibians, sauropsids and mammals are tetrapods. The ancestors of snakes, glass lizards and other limbless amphibians and sauropsids are tetrapods. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian. They are now a dominant part of the terrestrial fauna, representing all known larger land animals. Some groups have even returned to an aquatic existence, including the largest animal known, the blue whale.

Tetrapoda includes four classes: amphibians, reptiles, mammals and birds. Overall the biodiversity of tetrapods has grown exponentially over time from a single amphibian group sometime in the Devonian to many thousands of species today. The overall composition of biodiversity was driven primarily by amphibians in the Palaeozoic, dominated by reptiles in the Mesozoic and expanded by the explosive growth of birds and mammals in the Cenozoic. As biodiversity has grown so has the number of niches tetrapods occupied. The first tetrapods lived in waterside habitats and fed primarily on fish, today the Earth supports a great diversity of tetrapods that live in many habitats and subsist on a variety of diets.