We describe trends in illicit drug use revealed by the Australian Illicit Drug Reporting System (IDRS) between 1996 and 2006. We begin by briefly outlining the rationale, development, and testing of the IDRS, which integrates information from: interviews with a sentinel population of injecting drug users (IDU); key experts in health and law enforcement; and indicators that include information on drug purity and price, plus indicators of drug-related harm, such as fatal and nonfatal overdoses. These sources of information are critically discussed at annual meetings of researchers, policy makers and practitioners in the field. We describe what the IDRS has revealed about the use of heroin, cocaine, methamphetamines, and injected pharmaceutical preparations (opioids and benzodiazepines) over the period 1996–2006. We also illustrate how IDRS data can be combined with pharmaceutical prescription data to evaluate the effectiveness of policies designed to reduce benzodiazepine injecting. We also very briefly describe recent experience with monitoring trends on “dance party” drug use that extends the methods of IDRS by combining data from interviews with party drug users, key experts, and leading indicators of drug use.