Millions are caught and killed every year.
And some species that have been around since dinosaurs walked the Earth could soon die out altogether.
The scientists want sharks protected from fishermen in special marine reserves, like tuna, sea turtles and other large creatures.
But more and more people in China are eating shark's-fin soup.
And boats trying to catch other fish often kill sharks by mistake.
The great white, thresher, and tiger sharks are all under threat.
But hammerhead sharks have suffered the most.
Astonishingly there is only one surviving now for every 10 that were alive in 1986.