A squirrel is a small or medium-sized rodent of the family Sciuridae. In the English-speaking world, it commonly refers to members of this family's genera Sciurus and Tamiasciurus, which are tree squirrels that have large bushy tails, and are indigenous to Europe, Asia and the Americas. Similar genera are found in Africa.

The Sciuridae family also include flying squirrels, as well as ground squirrels such as the chipmunks, prairie dogs, and woodchucks.