Historically, nation states have had very different approaches to the imposition and implementation of life imprisonment. They range from total prohibitions on its use, to mandatory requirements for it to be imposed for certain offences and implemented in a way that allows no realistic prospect of release before the offender dies in prison – and many variations in between. Until relatively recently, these different approaches to life imprisonment did not create a major problem for international co-operation in criminal matters. In cases involving the extradition of criminal suspects or the transfer of sentenced prisoners - two staple forms of co-operation in an increasingly globalised world where crime control requires states to work together – states simply accepted each other’s approaches to this form of punishment and did not enquire too closely into what happened to extradited or transferred persons after they had been sent back.