Marine mammals are found in abundance in Arctic and Antarctic waters and a few species are specially adapted to living in very cold waters. However, the most numerous whale species are most common in the cold temperate zone where cold and warm currents meet. Many migrate to warmer waters in the winter when food is harder to get in the colder ecosystems. In fact Iceland lies where the cold and warm oceanic currents meet and consequently Icelandic waters are very rich in whales. At least 12 species of cetaceans occur regularly in Icelandic waters, 5 species of baleen whales and 7 species of toothed whales, including dolphins and porpoise. In addition, 11 species have been recorded more sporadically.

Many whale species have been seen in whale watching tours off northern Iceland but as most whale species are oceanic and avoid the coast some of them are quite rare. The blue whale (Balaenoptera musculus), bottlenose whales (Hyperoodon ampullatus) and killer whale (Orcinus orca) are examples of such oceanic animals, they are sometimes but not very often seen from whale watching boats. The sightings are also very irregular. Even more oceanic and more rare are fin whales (Balaenopters physalis), sei whales (Balaenopter borealis), sperm whales (Physeter macrocephalus) and pilot whales (Globicephala melas)

A few species are coastal and much more frequently seen. These are harbour porpoise (Phocoena phocaena), white beaked dolphins (Lagenorhynchus albirostris), minke whales (Balaenoptera acutorostrata) and humpback whales (Megaptera novaeangliae). The white beaked dolphin has a close relative, the white sided dolphin (Lagenorhynchus acutus) that is only found in warmer waters off southern Iceland.