A harrier is any of the several species of diurnal hawks forming the Circinae sub-family of the Accipitridae family of birds of prey. Harriers characteristically hunt by flying low over open ground, feeding on small mammals, reptiles, or birds.

Most harriers are placed in the genus Circus, the scientific name arising from the circling movements female and male make when courting. Two other harriers are in the genus Polyboroides, the harrier-hawks, which are allopatric (geographically separated) and restricted to the Afrotropic ecozone. The remaining single species forms the monotypic genus Geranospiza.