Mara Salvatrucha (MS-13), founded in 1980s Los Angeles by Salvadoran immigrant youth, is today one of the largest street gangs in North and Central America. In recent years the group has acquired a reputation for extreme brutality and has ostensibly mutated into a fast-expanding, transnational organized crime network with possible ties to international terrorists. Drawing on key concepts in gang research and multiple methodological tools, this article seeks to sharpen understanding of MS-13's structure and activities. While the group is active in many countries, it is transnational only in a symbolic manner, not in its configuration or span of authority. Impelled largely by Central American gang-suppression policies, MS-13 has evolved from a traditional street gang into a group with organized crime characteristics, but it remains a social phenomenon rooted in urban marginality. Ultimately, a more nuanced picture of Mara Salvatrucha can inform the search for more effective gang policies.