In biology, bilateral symmetry is a characteristic of multicellular organisms, particularly animals. A bilaterally symmetric organism is one that is symmetric about a plane running from its frontal end to its caudal end (head to tail), and has nearly identical right and left halves.

Most animals are bilaterally symmetric, including humans. The exceptions are sponges (no symmetry), jellyfish and ctenophores (radial symmetry), and echinoderms (partial radial symmetry; starfish exhibit pentamerism).

See also: radial symmetry