Fender skirts, known in Australia and the United Kingdom as spats, are pieces of bodywork on the fender that cover the upper portions of the rear tires of an automobile.

Fender skirts are implemented for both aesthetic and aerodynamic reasons. Rather than air flowing into and being trapped in the rear wheel well, it flows smoothly over the bodywork. They are typically detachable to allow for tire changes. Automakers have also experimented with front wheel fender skirts, as on the 1950-1954 Nash Rambler, but with success limited by the fact that the front wheels must pivot for steering, extending out from the side of the vehicle slightly.

First described as "pants", they were used for the streamlining effect by Frank Lockhart on a 1928 Stutz land speed record attempt car. Factory production of fender skirts began with the 1932 Graham-Paige. Aesthetically streamlined designs were copied to mass-produced models. The innovations introduced by Amos Northup, such as the V'd radiators, fender skirts, and sloping beaver-tails, became common after 1933. However, by the 1970s, fender skirts began to disappear from mass market automobiles. Fender skirts remained for some time longer on a few cars, particularly large American luxury cars.