Oniscidea subordo_authority = Latreille (Pierre Andr� Latreille), 1802 subdivision_ranks = Infraorders and Families (Family (biology)) subdivision = *Infaorder/Section Diplocheta ***Ligiidae *Infraorder Holoverticata **Section: Tylida ***Tylidae **Section: Microcheta ***Mesoniscidae **Section: Synocheta ***Schoebliidae ***Styloniscidae ***Titaniidae ***Trichoniscidae ***Turanoniscidae **Section: Crinocheta ***Bathytropidae ***Berytoniscidae ***Detonidae ***Halophilosciidae ***Olibrinidae ***Oniscidae ***Philosciidae ***Platyarthridae ***Pudeoniscidae ***Rhyscotidae ***Scyphacidae ***Speleoniscidae ***Sphaeroniscidae ***Stenoniscidae ***Tendosphaeridae ***Actaeciidae ***Armadillidae ***Armadillidiidae ***Atlantidiidae ***Balloniscidae ***Cylisticidae ***Eubelidae ***Periscyphicidae ***Porcellionidae ***Trachelipodidae ***Dubioniscidae ***Hekelidae ***Irmaosidae ***Pseudarmadillidae ***Scleropactidae

A woodlouse (known by many common names: see below (#Common names); plural woodlice) is a crustacean with a rigid, segmented, long exoskeleton and fourteen jointed limbs. Woodlice form the suborder Oniscidea within the order Isopoda, with over 3,000 known species.

Woodlice in the genus Armadillidium can roll up into an almost perfect sphere as a defensive mechanism, hence some of the common names (#Common names) such as pill bug or roly-poly. Most woodlice, however, cannot do this.