The house mouse (Mus musculus) probably has a world distribution more extensive than any mammal apart from humans. Its geographic spread has been facilitated by its commensal relationship with humans which extends back at least 8,000 years. They do considerable damage by destroying crops and consuming and/or contaminating food supplies intended for human consumption. They are prolific breeders, sometimes errupting and reaching plague proportions. They have also been implicated in the extinction of indigenous species in ecosytems they have invaded and colonised which are outside their natural range. An important factor in the success of the house mouse is their behavioural plasticity brought about by the decoupling of genetics and behaviour. This enables the house mouse to adapt quickly and to survive and prosper in new environments.