双髻鲨（学名：Sphyrnidae），又称丫髻鲨，是真鲨目的一科，种类不多，各种之间差异不大，头的前部向两侧突出，眼睛在突出部分的顶端，视野更有立体感，容易分辨远近，如同古代女子头上梳的双发髻。鱼体最大可达4.5米，性凶猛，以鱼类为主要食物，是一种食人鲨，常成群活动，互相用姿势语言交流，曾有报导达500条的群体，主要生活在热带和亚热带海洋水域，全世界都有分布。

双髻鲨繁殖是胎生或卵胎生，一次能生20多条幼鲨。

2007年5月，科学家经DNA鉴定，证实发现双髻鲨可以进行一种称为「孤雌生殖」的无性生殖行为，可以不透过雄性，而使自己的卵子受精，这是目前鲨鱼的首例。

The hammerhead sharks are a group of sharks in the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a cephalofoil. Most hammerhead species are placed in the genus Sphyrna while the winghead shark is placed in its own genus, Eusphyra. Many not necessarily mutually exclusive functions have been proposed for the cephalofoil, including sensory reception, maneuvering, and prey manipulation. Hammerheads are found worldwide in warmer waters along coastlines and continental shelves. Unlike most sharks, hammerheads usually swim in schools during the day, becoming solitary hunters at night. Some of these schools can be found near Malpelo Island in Colombia, Cocos Island off Costa Rica, and near Molokai in Hawaii. Large schools are also seen in the waters off southern and eastern Africa.