This paper summarises and compares the impacts of cannabis decriminalisation measures in two countries. In Australia, an expiation model of decriminalisation succeeded in avoiding the imposition of criminal convictions for many offenders, but substantial numbers of offenders received criminal convictions because of a general "net-widening" in cannabis offence detections, and the failure of many offenders to pay expiation fees and thus avoid criminal prosecution. Despite these problems, the expiation approach has been cost-effective, reducing enforcement costs without leading to increased cannabis use. In the United States, cannabis decriminalisation similarly reduced enforcement costs, with enforcement resources generally redirected toward trafficking and other illicit drugs. There were no increases in cannabis use or substantial problems that could be ascribed to decriminalisation. The implications for other countries are discussed, with particular attention to the importance of implementation issues, monitoring, and evaluation. Although decriminalisation has succeeded in reducing enforcement and other costs without increasing the problems associated with cannabis use, the same impacts would not necessarily result from the legalisation of cannabis or the decriminalisation of other illicit drugs.