Most of the empirical research on Central American street gangs, called maras, has been published only in Spanish. Reviewing that literature, the American scholarship on gangs, and the author's own research on Central American gangs from the mid-1990s, this article depicts the processes through which the maras (Mara Salvatrucha and the Eighteenth Street Gang) evolved from youth street gangs in the late 1980s to protection rackets with features of transnational organizations. Intense migratory flows between El Salvador, Guatemala, Honduras, and the United States, and the hard-line suppression policies against youth gangs in institutionally weak Central American countries created the conditions that prompted networking and organization among Central American street gangs. This article highlights the changes in the dynamics of violence and the transformations in the gangs' social spaces to illustrate the evolution of the maras. (Published Abstract)