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