The megalodon (/ˈmɛɡələdɒn/ MEG-ə-lə-don; from Greek: μέγας ὀδούς, "big tooth"), Carcharodon megalodon or Carcharocles megalodon (in dispute), was a giant shark that lived in prehistoric times. The oldest remains of this species found are about 18 million years old and C. megalodon became extinct in the Pleistocene epoch probably about 1.5 million years ago. It was the apex predator of its time and is the largest carnivorous fish known to have existed.

C. megalodon could grow more than 18 metres (59 ft) long and is also quite possibly the largest shark ever to exist. From scrutiny of its remains, scientists conclude that C. megalodon belongs to the order Lamniformes. However, scientists are still debating which genus would be most appropriate for C. megalodon from the two proposed. Fossil evidence has revealed that megalodon fed upon large marine animals.