Cannabis remains the most commonly used illicit drug in Australia, with an estimated five million people aged 14 and above having tried the drug. Typically, people begin using cannabis in their late teens or early twenties; thereafter, use steadily decreases. While most cannabis use is experimental or intermittent, it has been estimated that around one in ten people who try cannabis become dependent on it. This brief review of the evidence answering key questions in relation to cannabis was commissioned by the Australian National Council on Drugs for an audience including media, politicians and their advisers, the alcohol and other drugs sector, and interested members of the community. This review of the current research and clinical literature reflects the status of the evidence to November 2004.