Pufferfish are typically small to medium in size, although a few species such as the Mbu pufferfish can reach lengths greater than 50 cm (20 in).

Tetraodontiformes, or pufferfish, are most significantly characterized by their four beak-like teeth – hence the name combining the Greek terms “tetra” for four and “odous” for tooth. Each of the top and bottom arches is fused together with a visible midsagittal demarcation, which are used to break apart and consume small crustaceans. The lack of ribs, a pelvis, and pelvic fins are also unique to pufferfish. The notably missing bone and fin features are due to the pufferfish’ specialized defense mechanism, expanding by sucking in water through an oral cavity.

Pufferfish can also have many varied structures of caltrop-like dermal spines, which account for the replacement of typical fish scales, and can range in coverage extent from the entire body, to leaving the frontal surface empty.

Tetraodontidae typically have smaller spines than the sister family Diodontidae, with some spines not being visible until inflation.