Through the lens of Bourdieusian field theory, this article examines the transnationalization of the urban security field in contemporary Mexico City. It demonstrates that while the local bureaucratic field has held a monopoly over the definition of security issues, previously marginalized actors situated outside of the local security field used the political opportunity created by the intersection of the democratization of local politics, the neoliberalization of the Mexican economy and rising crime rates since the mid-1990s to deploy “internationalization strategies” to confront the bureaucratic field’s definitional authority over urban security. While the resulting struggles within the urban security field undermined the dominance of the bureaucratic field and contributed to a growing transnationalization of urban security governance, the analysis shows how, because of the “two-tiered” nature of the transnational urban security field, these processes did not improve the overall security situation in the city.