Nightjars are medium-sized nocturnal or crepuscular birds in the family Caprimulgidae and order Caprimulgiformes, characterised by long wings, short legs, and very short bills. They are sometimes called goatsuckers, due to the ancient folk tale that they sucked the milk from goats (the Latin for goatsucker is caprimulgus), or bugeaters, their primary source of food being insects. Some New World species are called nighthawks. The English word "nightjar" originally referred to the European nightjar.

Nightjars are found all around the world, with the exception of Antarctica and certain island groups such as the Seychelles. They can be found in a variety of habitats, most commonly the open country with some vegetation. They usually nest on the ground, with a habit of resting and roosting on roads.

The subfamilies of nightjars have similar characteristics, including small feet, of little use for walking, and long, pointed wings. Typical nightjars, though, have rictal bristles, longer bills, and softer plumage. The colour of their plumage and their unusual perching habits help conceal them during the day.