The hemipterans constitute one of the largest insect orders, and are the largest among the hemimetabolous insects, i.e. the insects with incomplete metamorphosis.

The hemipterans are a very diverse order, which encompasses three very different suborders: Heteroptera (the true bugs), Auchenorrhyncha (the plant hoppers, leaf hoppers, cicadas, and spittle bugs with more), and Sternorrhyncha (the aphids, scale insects, and whiteflies with more). Their main shared trait is the mouth parts, which form a segmented, beak-like rostrum adapted for sucking fluids. Most hemipterans feed on plant sap, but the true bugs include many predacious species plus a few adapted to sucking blood, including the notorious bedbug. Many plant-sucking hemipterans are serious pests on crops. Most of these belong to the Sternorrhyncha.