Today’s gangs are not only local, masculine, ethnic, and offline but also global, mixed, multiethnic, and online: they are (trans)gangs. This article presents the outcomes of the TRANSGANG Project, which has investigated youth street groups in twelve cities in Southern Europe, Northern Africa, and the Americas. The research approached transnational gangs as agents of mediation, focusing on experiences of conflict resolution from within the groups. After presenting three case studies of good practice analyzed in Barcelona (Catalonia, Spain), Rabat-Salé (Morocco), and Medellín (Colombia), the article discusses different models of mediation, including intra- and inter-group violent and nonviolent conflict resolution. It ends with a proposal for transforming the “Bermuda triangle” of gangs, in which youth street groups disappear or become invisible, imprisoned, or stigmatized, into a “Magic triangle,” in which youth street groups become visible, proactive, and recognized actors. (Trans)gangs have the power to mediate inside gangs, between gangs, and between gangs and society, improving the life worlds of excluded young people.