双翅目（学名：Diptera）包括蚊、蝇、虻等昆虫，约有8.5万种，是昆虫纲中居于鞘翅目、鳞翅目和膜翅目之后的第四大目。除了在南极洲之外，在全世界都很普遍。其中某些种类是传播疾病给人或其他动植物的媒介。另一方面，有关遗传学的知识和发展大都是根据对黑腹果蝇所做的实验所获得。

双翅目是属于完全变态的昆虫，也就是从无翅的蛆或孑孓经过化蛹后变为能够飞翔的成虫。牠们大多数以摄取液态的食物，例如腐败的有机物，或是花蜜或树汁等为时，而部分种类以吸取人类或动物的体液为食。另外某些种类以寄生或猎取其他昆虫为食，例如寄生蝇、食虫虻等。

True flies are insects of the order Diptera (from the Greek di = two, and ptera = wings). Diptera is a large order containing an estimated 1,000,000 species of mosquitoes, gnats, midges and others, although only 12% (about 120,000 species) have been described. It is one of the major insect orders with ecological and human importance. Mosquitoes (Culicidae) are vectors for malaria, dengue, West Nile virus, yellow fever, encephalitis, and other infectious diseases.