The basking shark is the second largest fish in the world, and like the largest fish (the whale shark) and the largest animal (the blue whale), basking sharks are filter feeders that eat tiny, planktonic prey. Reaching lengths of 40 feet (12 m) and resembling predatory sharks in appearance, the basking shark can give an intimidating impression, but they are quite harmless. They spend most of their time near the surface, swimming with their extraordinarily large mouths open, filtering out their preferred prey, but they may also make deeper, feeding dives.

The basking shark is one of a few species that lives in temperate latitudes, both north and south of the equator, but not between these two zones in the tropics. However, scientists believe that the individuals in these two zones are all the same species, so it is likely that at least some individuals (perhaps males) that spend part of the year in the deep sea move back and forth between the two hemispheres without ever coming to the surface. Throughout some parts of their range (e.g., both coasts of North America), basking sharks are uncommon and solitary, but during some seasons and places (e.g., the UK in the summer), they can be fairly common and form large groups.

After centuries of targeted fishing around Europe, the basking shark is considered vulnerable to extinction. While several countries have given them some or complete legal protection, legal fisheries still exist in other places, and occasionally, basking sharks are captured unintentionally in other fisheries. Shark scientists still have much work to do in order to find out more information about the life history, biology, and ecology of these giant fish.