This monograph (No. 11) reports on the work of the complex systems scientists at ANU. Complexity Theory is a loose cluster of theories and methodologies aiming at understanding the properties of complex adaptive systems. Complex adaptive systems (CAS) are ones characterised by: emergence; path dependency: non state equilibrium; and adaptation. The heroin drug market fits these characteristics nicely. The features of the agent-based model, called SimDrug, include the spatial environment, time scale, and social agents. SimDrug includes different types of social agents: users, dealers, wholesalers, police constables, and outreach workers. Each type represents a minimum set of characteristics and dynamics that allow the whole artificial population to display most of the properties observed in real societies. The model has proved robust and stable. SimDrug has demonstrated the plausibility of using a multi-agent system model to describe the
relationships between heroin users, dealers, their surroundings and the two interventions modelled (outreach workers and police). In future developments, we hope that policy makers will be able to use the model to determine potential scenarios as a result of their intervention.