Lemmings are small rodents, usually found in or near the Arctic, in tundra biomes. They are subniveal animals, and together with voles and muskrats, they make up the subfamily Arvicolinae (also known as Microtinae), which forms part of the largest mammal radiation by far, the superfamily Muroidea, which also includes rats, mice, hamsters, and gerbils.

Lemmings have become the subject of a widely popular misconception that they commit mass suicide when they migrate. It is not a mass suicide, but the result of their migratory behavior. Driven by strong biological urges, some species of lemmings may migrate in large groups when population density becomes too great. Lemmings can swim and may choose to cross a body of water in search of a new habitat. In such cases, many may drown if the body of water is so wide as to stretch their physical capability to the limit. This fact, combined with the unexplained fluctuations in the population of Norwegian lemmings, gave rise to the misconception.

The misconception of lemming "mass suicide" is long-standing and has been popularized by a number of factors. It was well enough known to be mentioned in "The Marching Morons," a 1951 short story by Cyril M. Kornbluth. In 1955, Disney Studio illustrator Carl Barks drew an Uncle Scrooge adventure comic with the title "The Lemming with the Locket". This comic, which was inspired by a 1953 American Mercury article, showed massive numbers of lemmings jumping over Norwegian cliffs. Even more influential was the 1958 Disney film White Wilderness, which won an Academy Award for Documentary Feature, in which staged footage was shown with lemmings jumping into certain death after faked scenes of mass migration. A Canadian Broadcasting Corporation documentary, Cruel Camera, found the lemmings used for White Wilderness were flown from Hudson Bay to Calgary, Alberta, Canada, where they did not jump off the cliff, but were in fact launched off the cliff using a turntable.

Lemmings do not hibernate through the harsh northern winter. They remain active, finding food by burrowing through the snow and using grasses clipped and stored in advance. They are solitary animals by nature, meeting only to mate and then going their separate ways, but like all rodents, they have a high reproductive rate and can breed rapidly when food is plentiful.