The common snook (Centropomus undecimalis) is a species of marine fish in the family Centropomidae of the order Perciformes. This species is native to the coastal waters of the western Atlantic Ocean and Caribbean Sea, from southern Florida and Texas to Rio de Janeiro in Brazil. The oo can be pronounced as in either room or good.

One of the largest snooks, Centropomus undecimalis grows to a maximum overall length of 140 centimetres (4.6 ft) and a maximum recorded weight of 24 kilograms (53 lb; 3.8 st). Of typical centropomid form, it possesses drab coloration except for a distinctive black lateral line. It can also possess bright yellow pelvic and caudal fins, especially during spawn.^{[citation needed]}

Occurring in shallow coastal waters (up to 20 metres (66 ft) depth), estuaries, and lagoons, the fish often enters fresh water. It is carnivorous, with a diet dominated by smaller fishes, and crustaceans such as shrimps, and occasionally crabs.

Common snook are protandric hermaphrodites, changing from male to female after maturation. This transition is identified by the presence of both male and female sex cells in the gonads and takes place when they grow to between 9.4-24 inches (24.0-82.4 cm) fork length which corresponds to 1-7 years of age. A study conducted in 2000, indicated that the sex ratios for common snook ages 0 - 2 are significantly skewed between the east and west coasts of Florida (USA) due to protrandry and differences in growth and mortality rates. The majority of small common snook are male and most large snook are female. Males reach sexual maturity during their first year at 5.9-7.9 inches (15.0-20.0 cm) fork length. Research shows that female gonads mature directly from the mature male gonads shortly after spawning. The probability that a common snook of a particular size will be a female increases with length or age.