The muskrat (Ondatra zibethicus), the only species in genus Ondatra, is a medium-sized semi-aquatic rodent native to North America, and introduced in parts of Europe, Asia, and South America. The muskrat is found in wetlands and is a very successful animal over a wide range of climates and habitats. It plays an important role in nature and is a resource of food and fur for humans, as well as being an introduced species in much of its present range.
The muskrat is the largest species in the arvicoline subfamily; which includes 142 other species of rodents, mostly voles and lemmings. Muskrats are called "rats" in a general sense because they are medium-sized rodents with an adaptable lifestyle and an omnivorous diet. They are not, however, so-called "true rats", that is members of the genus Rattus.