This text presents the key concepts of the TRANSGANG project, displayed as answers to seven research questions: what, when, who, why, where, how and what for.It starts by defining the conceptual triangle that the title frames: Transnational Gangs as agents of Mediation (What).The central chapters point out the historical context: Neoliberal States (When); the central subjects of study: Gangs (Who); the proactive approach: Mediation (Why); the border spaces to be investigated in the three regions: the Americas, North Africa and Southern Europe (Where); and the methodological perspective adopted (How).The final conclusive chapter explores the expected impact of the research, from resistance to resilience through empowerment (What For).The text includes a complete literature, ordered by topics and regions, and a specific Glossary.