Self-report offending surveys, such as the OCJS, are primarily designed to provide a better measure of the extent and nature of offending than can be obtained through official records. Data from the criminal justice agencies only provide a partial measure of offending because many offenders (and offences) are never formally processed. Moreover, most official data sources do not allow examination of the criminal careers of individual offenders. Two exceptions to this are the Home Office’s Offenders Index and the Police National Computer, both of which allow access to criminal conviction histories. Self report offending surveys ask people directly about their offending. Such surveys therefore include offenders and offences that are not dealt with by the criminal justice system and also enable patterns of offending and the factors associated with different forms of offending behaviour to be examined. However there are some limitations and key methodological issues that need to be considered in interpreting the findings presented in this report.