In 1989 the Crime Research Centre (University of Western Australia) and criminal justice agencies in Western Australia became involved in the INOIS (Integrated Numerical Offender Identification System) project. The principal aim of this project was to introduce a common, unique identifier for offenders so that a longitudinal database could be established that could ''track '' offenders through the criminal justice system. This paper explains reasons for establishing this kind of database and explores some of the conceptual and technical issues which arise. Central to the development of the database and, therefore, to the INOIS project, was the underlying need to uniquely identify each offender. This paper focuses on how record-linking techniques were used to achieve this. The record-linking component of the INOIS project is discussed at length, and results from trials and from preliminary runs of the linkage system are presented and discussed Additional research and operational usages of such a system are also identified.