Esox is a genus of freshwater fish, the only living genus in the family Esocidae — the esocids which were endemic to North America, Europe and Eurasia during the Paleogene through present.

The type species is E. lucius, the northern pike. The species of this genus are known as pike and pickerel, and in heraldry they are usually called lucy.

The big pike species are native to the Palearctic and Nearctic ecozones, ranging across northern North America and from Western Europe to Siberia in Eurasia. They have been found in many urban lakes in Western Europe, reported to be in the Rostrum (Lucerne) and the Serpentine, (London).

Pike can grow to a maximum recorded length of 1.83 metres (6 ft 0 in), reaching a maximum recorded weight of 35 kilograms (77 lb). The UK record pike of 21 kilograms (46 lb) was caught on a Creek Chub Pikie lure by Roy Lewis at Llandegfedd Reservoir in Wales in 1992. Individuals have been reported to reach 30 years in age. All pike over 5 kilograms (11 lb) in body weight are females. They have the elongated, torpedo-like form of predatory fishes, with sharply-pointed heads and sharp teeth. Their coloration is typically grey-green with a mottled or spotted appearance with stripes along their back, perfectly camouflaged among weeds. Individual pike marking patterns are unique, like fingerprints.