The grey reef shark, Carcharhinus amblyrhynchos (sometimes misspelled amblyrhynchus or amblyrhinchos), is a species of requiem shark, family Carcharhinidae. One of the most common reef sharks in the Indo-Pacific, it is found as far east as Easter Island and as far west as South Africa. This species is most often found in shallow water near the drop-offs of coral reefs. The grey reef shark has a typical "reef shark" shape with a broad, round snout and large eyes. This species can be distinguished from similar species by the plain or white-tipped first dorsal fin, the dark tips on the other fins, the broad black rear margin on the tail fin, and the lack of a ridge between the dorsal fins. Most individuals are less than 1.9 m (6.2 ft) long.

Grey reef sharks are fast-swimming, agile predators that feed primarily on free-swimming bony fishes and cephalopods. Their aggressive demeanor enables them to dominate many other shark species on the reef, despite their moderate size. Many grey reef sharks have home ranges on a particular area of the reef, to which they will return time and again. However, they are not territorial but are rather quite social. During the day, these sharks often form aggregations of 5–20 individuals near coral reef drop-offs, which split up in the evening as the sharks begin to hunt. Adult female grey reef sharks also form groups in very shallow water, where the higher water temperature may accelerate their growth or that of their unborn young. Like other members of their family, the grey reef shark is viviparous, meaning that the mother nourishes her embryos via a placental connection. Litters of 1–6 pups are born every other year.

Grey reef sharks were the first shark species known to perform a threat display, a stereotyped behavior warning that it is prepared to attack.The display involves a "hunched" posture with characteristically dropped pectoral fins, and an exaggerated, side-to-side swimming motion. Grey reef sharks will often perform the display if they are followed or cornered by divers, to indicate that they perceive a threat. This species has been responsible for a number of attacks on humans and should be treated with caution, especially if they begin displaying. Grey reef sharks are caught by many fisheries and susceptible to local population depletion due to their low reproductive rate and limited dispersal. As a result, the World Conservation Union has assessed this species as Near Threatened.