Since the 1990s, the office market in Mexico City has been fundamentally transformed. The available office space doubled since 1997 to 6.9 mill.m(2), with the first class segment capturing 80\% of the construction activity. In addition, the geography of the office market has been altered, because new centers of property development have been created in the Western parts of the city. The paper goes on to argue that the transformation of the office market is basically driven by processes of global city formation, because ever more global corporations have a (regional) headquarter in Mexico City, what has caused a sharp increase in the demand for first class office spaces. In the second part of the paper it is maintained that the transformation of the office market and of urban spaces in Mexico City are best understood as ``tansnationalization{''}. Taking the Torre Mayor as a case study it is shown that the new global city spaces are produced and used principally by actors without a clear national identity. In addition, they have been built according to new mechanisms of planning (Strategic Planning), which correspond to a new global standard. Accordingly, it is sustained that the rules of urban planning and management are becoming denationalized, too.