Swordfish are large, highly migratory, predatory fish characterized by a long, flat bill. They are the sole member of their extended family Xiphiidae. They are elongated, round-bodied, and lose all teeth and scales by adulthood. They can reach a maximum size of 177 inch (455 cm) and 1,400 lb (650kg). The International Game Fish Association's all-tackle angling record for a swordfish was a 1,182 lb (536.15 kg) specimen caught off Chile in 1953.
The swordfish is named after its sharp beak resembling a sword (latin: gladius), which together with its streamlined physique allows it to cut through the water with great ease and agility. Contrary to popular belief, the "sword" is not used to spear, but instead may be used to slash at its prey in order to injure it  and make for an easier catch. Mainly the swordfish relies on its great speed, as it is capable of reaching speeds up to 50 mph (80 km/hr), and its agility in the water to catch its prey. One possible use for the sword-like bill is for protection from its few natural predators., such as the shortfin mako shark, which is one of the rare sea creatures large and fast enough to chase down and kill an adult swordfish. Sometimes in the struggle with a shark a swordfish can kill it by ramming it in the gills or belly. Females grow larger than males, with males over 300 lb (135 kg) being rare. Females mature at 3-5 years of age (depending of the geographical areas), and spawning occurs on ly in water warmer than 24 °C. Reproduction can take place year round in the equatorial Pacific, and from March to July elsewhere.

Adult swordfish's diet includes pelagic fish such as small tuna, dorado, barracuda, flying fish, mackerel, as well as benthic species of hake and rockfish. Squid are an important source of food when available. Swordfish are thought to have few predators as adults, although juveniles are vulnerable to predation by larger pelagic fish. They are cold blooded animals, qnd possess special organs next to their eyes to heat their eyes and their brain. Temperatures of 10 to 15 °C above the surrounding water temperature have been measured. The heating of the eyes greatly improves the vision, and subsequently ameliorates their ability to catch prey. Out of the 25 000 recorded species of bony fish, only 22 are known to have the ability to heat selected body parts above the temperature of the surrounding water. These include the swordfish, marlin, and tuna.

Swordfish are not schooling fish. They swim alone or in very loose aggregations, separated by as much as 10 meters from a neighbouring swordfish. They are frequently found basking at the surface, airing their first dorsal fin. Boaters report this to be a beautiful sight, as is the powerful jumping for which the species is known. This jumping, also called breaching, is thought by some researchers to be an effort to dislodge pests, such as remora or lampreys. It could also be a way of surface feeding by stunning small fish as they jump out of the water, making the fish more easily captured for food. Swordfish feed daily, most often at night when they rise to the surface and near-surface waters in search of smaller fish. They have been observed moving through schools of fish, thrashing their swords to kill or stun their prey and then quickly turning to consume their catch. In the western North Atlantic, squid is the most popular food item consumed. However fish such as menhaden, mackerel, bluefish, silver hake, butterfish, and herring also contribute to the swordfish's diet. The adults have few natural enemies, with the exception of large sharks, sperm whales, and orcas. They are easily frightened by small boats, yet paradoxically, large craft are often able to draw very near without scaring them. This makes swordfish easy to harpoon. The swordfish is often mistaken for other billfish (like marlin), but their physiology is quite different upon examination.