Hemiptera ( /hɛˈmɪptərə/) is an order of insects most often known as the true bugs (cf. bug), comprising around 50,000–80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others. They range in size from 1 millimetre (0.04 in) to around 15 centimetres (6 in), and share a common arrangement of sucking mouthparts. Sometimes the name true bugs is applied more narrowly still to insects of the suborder Heteroptera only.

The defining feature of hemipterans is their possession of mouthparts where the mandibles and maxillae have evolved into a proboscis, sheathed within a modified labium to form a "beak" or "rostrum" which is capable of piercing tissues (usually plant tissues) and sucking out the liquids — typically sap.

The forewings of Hemiptera are either entirely membranous, as in the Sternorrhyncha and Auchenorrhyncha, or partially hardened, as in most Heteroptera. The name "Hemiptera" is from the Greek ἡμι- (hemi; "half") and πτερόν (pteron; "wing"), referring to the forewings of many heteropterans which are hardened near the base, but membranous at the ends. Wings modified in this manner are termed hemelytra (singular: hemelytron), by analogy with the completely hardened elytra of beetles, and occur only in the suborder Heteroptera. The forewings may be held "roofwise" over the body (typical of Sternorrhyncha and Auchenorrhyncha), or held flat on the back, with the ends overlapping (typical of Heteroptera). In all suborders, the hindwings - if present at all - are entirely membranous and usually shorter than the forewings.