Following a historical review of restrictions on and penalties for illegal cannabis use, the paper looks at the effects of cannabis. These effects include pharmacological changes, tolerance and dependence, health risks, respiratory effects, cardiovascular effects, reproductive effects, psychological effects, changes in psychomotor functioning, changes in cognitive functioning and motivation, and psychiatric disorders. The paper examines the significance of the cannabis problem and attitudes toward its use, trends in the use of cannabis and other illegal drugs, the issue of decriminalization, the size and economic significance of the cannabis market in Queensland, and the law enforcement response to drug offenses involving cannabis. Issues to be addressed in the future are noted, including cannabis policy and legislation, drug law enforcement, and drug education. Appendixes contain a critical review of research on biological and psychological effects of cannabis and a learning curve model of the cannabis market. References, tables, and figures