The criminal justice system is a complex process involving police, courts and corrections. Historically these component parts have tended to act autonomously yet their actions impact on each other. Increasingly criminal justice policy makers have come to recognise the need to understand the long term impacts of policy changes across the whole system. To effectively and eficiently manage the criminal justice system, policy makers require analytical tools to project the relative effects of changes to policies based on current system information. Simulation models potentially offer a mechanism for assessing the short and long term effects of policies. This paper describes the devleopment of the Queensland Juvenile Justice Simulation Model (QJJSM), which is currently being used in the Queensalnd juvenile justice system.