Rising criminality and violence in key neighborhoods surrounding Mexico City’s historic center have limited easy access to downtown public spaces that used to host much of the city’s social, commercial, and political life. In 2002 a group of powerful local businessmen hired the international security consultant Rudolph Giuliani to design security measures that might remedy the city’s crime problems. The Giuliani plan not only called for restrictions on free movement and intense scrutiny of public behavior associated with the strategy of “zero tolerance” but also suggested the criminalization of certain behaviors and made recommendations for police reform that called into question the distinction between public and private police. One of the principal consequences of its implementation was to circumscribe public access to downtown space. Stated simply, the widening of downtown’s public sphere brought a narrowing of access to it along class lines. An examination of the context in which the plan was pursued traces the Giuliani invitation to the dynamics of downtown real estate development and land-use collusion between elected officials and private developers in the name of security policy.