Hemiptera (; from Ancient Greek hemipterus 'half-winged') is an order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, and shield bugs. They range in size from 1 mm (0.04 in) to around 15 cm (6 in), and share a common arrangement of piercing-sucking mouthparts. The name "true bugs" is often limited to the suborder Heteroptera.

Entomologists reserve the term bug for Hemiptera or Heteroptera, which does not include other arthropods or insects of other orders such as ants, bees, beetles, or butterflies. In some variations of English, all terrestrial arthropods (including non-insect arachnids, and myriapods) also fall under the colloquial understanding of bug.

Many insects with "bug" in their common name, especially in American English, belong to other orders; for example, the lovebug is a fly and the Maybug and ladybug are beetles. The term is also occasionally extended to colloquial names for freshwater or marine crustaceans (e.g. Balmain bug, Moreton Bay bug, mudbug) and used by physicians and bacteriologists for disease-causing germs (e.g. superbugs).

Most hemipterans feed on plants, using their sucking and piercing mouthparts to extract plant sap. Some are bloodsucking, or hematophagous, while others are predators that feed on other insects or small invertebrates. They live in a wide variety of habitats, generally terrestrial, though some are adapted to life in or on the surface of fresh water (e.g. pondskaters, water boatmen, giant water bugs). Hemipterans are hemimetabolous, with young nymphs that somewhat resemble adults. Many aphids are capable of parthenogenesis, producing young from unfertilised eggs; this helps them to reproduce extremely rapidly in favourable conditions.

Humans have interacted with the Hemiptera for millennia. Some species, including many aphids, are significant agricultural pests, damaging crops by the direct action of sucking sap, but also harming them indirectly by being the vectors of serious viral diseases. Other species have been used for biological control of insect pests or of invasive plants. A few hemipterans have been cultivated for the extraction of dyestuffs such as cochineal and carmine, and for shellac. The bed bug is a persistent parasite of humans, and some kissing bugs can transmit Chagas disease. Cicadas have been used as food, and have appeared in literature since the Iliad in Ancient Greece.