More than 50% of the world's population can today be defined as "urban": in fact, the new millennium has already seen the world's urban population "overtake" the rural one. Hoever, the challenge facineg 21st century is that of overcoming those spatial imbalances which lead to mere complex inequalities between the world's wealthy North and the poor South. Furthermore, we should not overlook the phenomena of cultural separation, or rather of conflict between the urban and rural areas. Lastly, we should also consider the growing phenomenon of counter-urbanisation in the recent organisation of space. This in noe a feature of all economically mature regions, contrasting, to a centain extent,with the trend of general urbanisation on a planetary scale.