A grouper fish is a type of fish that belongs to the subfamily Epinephelinae of the family Serranidae, in the order Perciformes. Not all serranids are called "groupers"; the family also includes the sea basses. The common name "grouper" is usually given to fish in one of two large genera: Epinephelus and Mycteroperca. In addition, the species classified in the small genera Anyperidon, Cromileptes, Dermatolepis, Graciela, Saloptia, and Triso are also called "groupers." Fish in the genus Plectropomus are referred to as "coral groupers." These genera are all classified in the subfamily Epiphelinae.

Groupers are carnivores, and they readily eat smaller fish, including other groupers. They also feed on invertebrates, such as octopuses and crustaceans. Groupers are typically stout fish with a large mouth and an equally large body. They have multiple rows of teeth. Groupers can come in a range of sizes, from small enough to be kept in aquaria to incredibly large, such as the goliath grouper (Epinephelus itajara) of the tropical Atlantic Ocean and the Queensland grouper (E. lanceolatus) of the Great Barrier Reef.

The meat of a grouper is delicious, which has become problematic as too many species are now overfished. Many groupers are important food fish, and some are now farmed. Unlike most other fish species, which are chilled or frozen, groupers are usually sold alive in markets. Some species are popular game fish for sea-angling.