Background: There are different street substance users' communities (SSUCs). Typology of SSUCs in Tehran, Iran was approached in this qualitative study.Methods: Using content analysis and saturation principles, 22 street-outreach workers were recruited and interviewed. Data were analyzed using open, axial, and selective coding.Findings: Three types of SSUCs were identified. SSUCs were different in geographic location, the community hierarchy, roles of residents and its function during a 24-hour period. Type 1: surrounded naturally by trees, mountains etc. or located in places like canals that make them not simply reachable, a nonresident smuggler (or a small group of smugglers) has the most power in its hierarchy, works 24 hours with at least two shifts, structured with special roles (nonresident smuggler, the Balancer, sex-worker, seller, armed guard, resident substance users and nonresident costumers). Type 2: mostly located in the city gardens, several nonresident smugglers with limited power, works 16 hours or less in a day, semi-structured with roles of nonresident drug dealer, sex-worker, resident substance users and nonresident costumers. Type 3: houses that their landlords are the resident drug dealers and let the costumers to use drug in the house. The substance users have to leave the house after using drug. The house is open less than 24 hours a day.Conclusion: Strategies for delivering harm reduction services in different types of SSUCs should be modified according to characteristics of these communities.