The European Otter is the most widely distributed otter species, its range including parts of Asia and Africa as well as being spread across Europe.

The European Otter's diet mainly consists of fish but can also include birds, insects, frogs, crustaceans and sometimes small mammals, including young beavers. In general this opportunism means they may inhabit any unpolluted body of freshwater, including lakes, streams, rivers, and ponds, as long as there is good supply of food. European Otters may also live along the coast, in salt water, but require regular access to freshwater to clean their fur. When living in the sea individuals of this species are sometimes referred to as "sea otters", but they should not be confused with the true sea otter, a North American species much more strongly adapted to a marine existence.

European Otters are strongly territorial, living alone for the most part. An individual's territory may vary between about one and forty kilometres long (about half to 25 miles), with about 18 km (about 11 miles) being usual. The length of the territory depends on the density of food available and the width of the water suitable for hunting (it is shorter on coasts, where the available width is much wider, and longer on narrower rivers). The territories are only held against members of the same sex, and so those of males and females may overlap. Males and females will breed at any time of the year, and mating takes place in water. After a gestation period of about 63 days, one to four pups are born, which remain dependent on the mother for a year. The male plays no direct role in parental care, although the territory of a female with her cubs is usually entirely within that of the male. Hunting mainly takes place at night, while the day is usually spent in the European Otter's holt (den) – usually a burrow or hollow tree on the riverbank which can sometimes only be entered from under water.