The Air Protection Act sets the division of the territory of the Czech Republic into zones and agglomerations with the purpose to assess and evaluate the level of ambient air quality. This chapter is devoted to more detailed evaluation of ambient air quality in the agglomeration of Prague, in the agglomeration of Brno and in the agglomeration of Ostrava/Karviná/ Frýdek-Místek, i.e. in the areas with deteriorated ambient air quality caused mainly by loads from traffic and industry. Moreover, these areas are densely populated; the share of inhabitants exposed to abovethe-limit concentrations is thus not negligible.