The Syngnathidae are a family of fish which includes the seahorses, the pipefishes, and the weedy and leafy sea dragons. The name is derived from Greek, syn meaning fused or together, and gnathus meaning jaws. This fused jaw trait is something the entire family has in common.

Syngnathids are found in temperate and tropical seas across the world. Most species inhabit shallow, coastal waters, but a few are known from the open ocean, especially in association with sargassum mats. They are characterised by their elongated snouts, fused jaws, the absence of pelvic fins, and by thick plates of bony armour covering their bodies. The armour gives them a rigid body, so they swim by rapidly fanning their fins. As a result, they are relatively slow compared with other fishes, but are able to control their movements with great precision, including hovering in place for extended periods.

Many syngnathid species are threatened due to human activities in their environment and overfishing. The main reasons for them being collected are the sale as curio and their use in traditional Chinese medicine as a tonic, to delay ageing and for their supposed aphrodisiac power, which could lead them to extintion.

Seahorses and pipefish are very popular with divers, for their beauty, their strange shape, and their amazing life history.

Pipefish look like straight-bodied seahorses with tiny mouths. The name is derived from the peculiar form of their snout, which is like a long tube, ending in a narrow and small mouth which opens upwards and is toothless. The body and tail are long, thin, and snake-like. They have a highly modified skeleton formed into armored plating. This dermal skeleton has several longitudinal ridges, so that a vertical section through the body looks angular, not round or oval as in the majority of other fishes.

A dorsal fin is always present, and is the principal (in some species, the only) organ of locomotion. The ventral fins are constantly absent, and the other fins may or may not be developed. The gill openings are extremely small and placed near the upper posterior angle of the gill cover.