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.

Pikes 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. 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). There are currently six recognized species in this genus: There is one fossil species, Esox kronneri Grande, 1999 known from the Eocene of the Green River formation.

The generic name Esox (pike fish) derives from the Greek ίσοξ (a kind of fish), itself a word of Celtic origin related to the Welsh eog and Irish Gaelic iasc (fish). Pliny uses the Latin form esox in reference to a large fish in the Rhine normally identified with lax (salmon). It is likely that Carolus Linnaeus's application of Esox to the pike is thus a misnomer.

The English common name "pike" is an apparent shortening of "pike-fish", in reference to its pointed head, Old English píc originally referring to a pickaxe. The plural of pike is pike.

A northern English and Lowland Scots name for the pike, ged, similarly derives from Old Norse gaddr (spike) (cf. the modern Swedish name for the pike, gädda, the Danish "gedde", the Norwegian "gjedde" and Scottish Gaelic: geadais). The Dutch name for the pike (snoek) has been given to a wide variety of fish reminding sailors of the pike (see snoek, snook).

The English "pike" originally referred specifically to the adult fish, the diminutive form "pickerel" (now used to name some of the smaller pike, E. americanus and E. niger) referring to the young. The walleye (Sander vitreus) is sometimes called a pickerel by Gerard, but it is unrelated to the pike, being a member of the perch family (family Percidae). Pike are not to be confused with the unrelated pikeminnows (traditionally, and perhaps better, known as squawfish) of genus Ptychocheilus (family Cyprinidae) or pikeperch (Sander lucioperca) which is more akin to walleye than to pike. Pike are also called "Jackfish" in North America and informally "Slough Shark" in Western Canada.

Pike feed on a wide range of food sources, predominantly smaller shoal fish. Pike are also cannibalistic, sometimes preying upon smaller members of their own species.

They will also prey on insects and amphibians such as newts or frogs in times when their usual food is scarce, and occasionally on small mammals like moles or mice when caught water-borne. Small birds such as ducklings may become a target for hungry pike. Pike are also known to prey on swimming snakes.

They are, however, undeserving of their reputation for being overly vicious predators. There are few substantiated incidents of pike 'attacks' on people. Pike's further reputation as a pest seems to lie predominately amongst anglers who seek more desirable species.

Effective methods for catching this hard-fighting fish include dead baits, live baits, and lure fishing. Pike can easily be damaged when handled since they are not as robust as their reputation would suggest. Colour of lure can be influenced by water clarity and weather conditions. Since pike have numerous sharp teeth it is wise to take extreme care when unhooking them. The use of a wet leather gauntlet and surgical forceps to remove hooks is highly recommended on safety grounds. If practising catch and release fishing, care for the pike should be the pike angler's utmost concern. The formerly recommended practice of grasping a pike by its eye sockets (tragically interpreted as "its eyes") resulted in countless released pike that quickly died from inability to see prey any longer.

The current recommended method of grasping pike is to close the hand firmly over the gill covers, and to make the period of handling as short as possible before release. Grabbing a pike by the gill covers is not feasible when a pike is very big, but it is easy to handle a pike by inserting the fingers at the bottom of the gill opening and grabbing the lower jaw. Big pike should also be supported at the belly. When a pike is held this way it is also easier to keep the mouth open to remove a hook. Many anglers now use special grips to grab the pike's front lower jaw, which can add to the safety of an anglers because of the danger imposed by the hooks of the lure or tackle and the pike's teeth. The Pike Anglers Club was formed in 1977 to campaign for the preservation of pike and the sport of pike fishing.

A practice known as gut hooking was previously widely used in catching pike. Upon taking the bait, the pike will hold it for a short time in its mouth as it moves off. The pike will then, usually, turn the bait in its mouth, so that it sits in alignment with its throat to ease swallowing. It is recommended that when pike fishing the process is not allowed to go this far and a strike is recommended as soon as a bite is indicated. Otherwise, what is known as gut hooking will result, which will normally kill or seriously injure the fish. Dutch research shows that cutting the line immediately when the fish is gut hooked will still give low mortality (14%). The hooks in the gut or stomach were either encapsulated or removed from the body. Placing hooks near the rear of the bait reduces the risk of deep hooking. Other methods of catching and handing pike that are now frowned upon are the gaff and the gag. The gaff is a metal hook on the end of a pole used to hook through the fish's body in place of a more humane landing net. A gag is a device for holding open the pike's mouth whilst unhooking. These are now illegal in Scotland, as they put a huge amount of pressure on a pike's jaw, thus causing irreparable damage.

Russian mythology holds that the pike is one of several forms assumed by evil water spirits called vodyanoy, and a ravenous mythical pike is traditionally blamed for decimating the fish population in the Sheksna River. Russian fairy tales, on the other hand, also tell about an old wise pike that can fulfil wishes of the one who catches it, if its catcher releases it back into its habitat. In the Finnish Kalevala, Väinämöinen creates a kantele (string instrument) from the jawbone of the pike.

Two United States Navy submarines have been named Pike, SS-6 of 1903 and SS-173 of 1935, and three, SS-22 of 1912, SS-177 of 1936, and SS-524 of 1944, named Pickerel. In addition, the Soviet submarines known to NATO as the Victor III class were called the Shchuka (Щука, "pike") class, in Russian. The Soviet Iosif Stalin tank (IS-3) was also nicknamed Shchuka, in reference to its sharply pointed hull front.

In heraldry, the pike is called a lucy. It is usually blazoned either naiant (swimming), embowed (bowed) or hauriant (jumping), though pairs of lucies may appear addorsed (back to back), as in the arms of the Finnish town of Uusikaupunki, Finland. (Argent, two lucies addorsed azure).