Urban and regional planning is frequently making use of the idea of public space; but, its actual social and political impact is very much debated. A geographical approach can help in clarifying the major aspects which are constraining its use. First, we note that the idea of public space rests on a set of myths which are related to the ideas of modernity, justice, democracy, rationality and the self. However, public space does not operate according to mythical modalities, because it requires norms and rules which draw on the rationality of the subject. Furthermore, it is not a space without material, social or cultural characteristics. On the contrary, it is a place which is both material and immaterial and which draws on imagination and on the narrative activity of the subject.