Research funded by NIDA points to the importance of studying drug abuse as the behavior of individuals in their environments. Although direct settings of drug abusers have received considerable research attention, less consideration has been given to indirect environmental influences. Understanding the structure of local drug markets and drug user's activities within these markets has potential for expanding prevention interventions. This experimental research represents a novel analytic perspective for understanding this less explored, yet extremely important, dimension of drug abuse with a computer-based social simulation of a local heroin market based on an already collected ethnographic data set. By simulating one heroin dealing market, the objective is to demonstrate that methods are feasible and can produce meaningful results. The long term goal of this project is to utilize the simulation created as a template for future illegal market simulations eventually leading to the development of a "simulated economic system." Simulating a local heroin market will be useful to researchers and policymakers to understand the self-organizing behaviors of drug users and identify the outcomes of these systems. The specific aims of this experimental project are to: 1. Construct a computer application that simulates a local heroin dealing market based on 18 months of ethnographic data previously collected by the applicant about this market, as well as a mid-level heroin dealing organization that operated within it. 2. Experiment with the computer application and manipulate its parameters and components. 3. Rigorously document the simulation modeling procedure: a. To note the strengths and weaknesses as a method for research on drug dealing. b. Recommend how future research can be designed to facilitate simulating other drug related behaviors. 4. Disseminate simulation results, project information, and programming notes to encourage and facilitate further research using this technology in the study of illegal drug use behaviors.