Small to medium-sized flies, 1-10 mm long. Male antenna usually plumose. Wing narrow. Legs long and slender. Male abdomen usually long and slender; terminalia not inverted. Larva apneustic, long, narrow, cylindrical, with strongly sclerotized nonretractile head capsule, and usually with pairs of anterior and posterior prolegs bearing spines or claws. Pupa somewhat comma-shaped, with enlarged cephalothorax and with dorsoventrally flattened abdomen usually bearing apically a pair of flattened lobes; leg sheaths usually curved under wing pads but sometimes extending posteriorly.