The morphology and biology of sucking lice (Anoplura) and biting lice (Mallophaga) are described. A table shows the main species for given hosts and provides simplified keys for identification. Lice have a direct pathogenic effect (damage to skin and cutaneous appendages, fall in productivity) and an indirect effect (transmission of Rickettsia prowazeki, R. quintana and Borrelia recurrentis in human beings; African and classical swine fever virus, equine infectious anaemia virus and Dipylidium caninum in animals). Control methods, current active insecticides (and those being tested) and appropriate formulations are outlined.