Porcupine, herbivorous rodent that has long, pointed spines, or quills, growing from the back and sides and, in some species, from the head and tail. The quills, which have needle-sharp ends containing hundreds of barbs, can be erected by the muscles of the skin. Their loose attachment and ready removal have given rise to the popular but incorrect idea that the animal can project its quills like arrows or darts.

The Eurasian porcupines range through the forests of southern Europe and Asia, Africa, and Indonesia. They are typified by the common porcupine, which is thick-bodied, grizzled, and black in colour. It grows to a length of at least 60 cm (24 in), with some of its quills exceeding 30 cm (12 in) in length. The American porcupines include four genera: the tree porcupines of Central and South America, the North American porcupine, the thin-spined porcupine of Brazil, and the Amazonian porcupine. The North American porcupine is found in heavily wooded regions from Alaska to the northern extreme of Mexico. It grows to a length of 65 to 80 cm (26 to 31 in) and has a short tail and brownish hair, which almost conceals its 5- to 15-cm (2- to 6-in) quills.

Scientific classification: Eurasian porcupines make up the family Hystricidae. American porcupines make up the family Erethizontidae. The common porcupine is classified as Hystrix cristata. Tree porcupines make up the genus Coendou. The North American porcupine is classified as Erethizon dorsatum, the thin-spined porcupine as Sphiggurus villosus, and the Amazonian porcupine as Echinoprocta rutescens.