The Molossidae, or free-tailed bats, are a family of bats within the order Chiroptera. The Molossidae is the fourth-largest family of bats, containing about 110 species as of 2012. They are generally quite robust, and consist of many strong-flying forms with relatively long and narrow wings with wrinkled lips shared through their genus. Their strong flying form allows them to fly 60 miles per hour using tail winds and at altitudes over 10,000 feet. This makes them unique among bats, as they are the only bat family that withstands the elevation. They are widespread, being found on every continent except Antarctica. They are typically found in caves, abandoned mines, or tunnels.

Bats are flying mammals of the order Chiroptera. With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most birds, flying with their very long spread-out digits covered with a thin membrane or patagium. The smallest bat, and arguably the smallest extant mammal, is Kitti's hog-nosed bat, which is 29–34 millimetres in length, 150 mm (6 in) across the wings and 2–2.6 g in mass. The largest bats are the flying foxes, with the giant golden-crowned flying fox reaching a weight of 1.6 kg and having a wingspan of 1.7 m.