Basking sharks are one of the largest sharks of the world's temperate oceans. Only the mighty whale shark is bigger. Despite a superficial similarity to the fearsome great white shark and a massive jaw one metre wide, basking sharks are actually harmless filter feeders. They use more than 5,000 gill rakers to strain plankton from around 1.5 million litres of water per hour. Basking sharks are born travellers, covering large distances in search of food, at the very leisurely pace of only three miles per hour. There is only one species of basking shark.

The basking shark (Cetorhinus maximus) is the second largest living fish, after the whale shark, and the second of three plankton-eating sharks, the other two being the whale shark and megamouth shark. It is a cosmopolitan migratory species, found in all the world's temperate oceans. It is a slow moving filter feeder and has anatomical adaptations to filter feeding, such as a greatly enlarged mouth and highly developed gill rakers. The shape of its snout is conical and the gill slits extend around the top and bottom of its head. The gill rakers are dark and bristle-like and are used to catch plankton as water filters through the mouth and over the gills. The basking shark is usually greyish-brown in color with mottled skin. The caudal (tail) fin has a strong lateral keel and a crescent shape. The teeth of the basking shark are very small and numerous and often number one hundred per row. The teeth themselves have a single conical cusp, are curved backwards and are the same on both the upper and lower jaws.

Basking sharks are a migrating species and are believed to overwinter in deep waters. They may occur in either small schools or alone. Small schools in the Bay of Fundy and the Hebrides have been seen swimming nose to tail in circles in what may be a form of mating behavior. Despite their large size and threatening appearance, basking sharks are not aggressive and are harmless to people. It has long been a commercially important fish, as a source of food, shark fin, animal feed, and shark liver oil. Overexploitation has reduced its populations to the point where some have disappeared and others need protection.