Armadillidiidae is a family of woodlice, a terrestrial crustacean group in the order Isopoda. Unlike members of other woodlouse families, members of this family can roll into a ball, an ability they share with the outwardly similar but unrelated pill millipedes and other animals. It is this ability which gives woodlice in this family their common name of pill bugs or roly poly. The best known species in the family is Armadillidium vulgare, the common pill bug.