Some reflections on this very special activity which consists in depositing in the urban space, open to all and generally outside (although spaces meeting the same criteria can also be interior) objects called" sculptures ". Are they of a definite type, recognizable among the other objects of the city? What meanings do they have? If the same object is in a museum, is its meaning identical? Where are they located in the city? Who chooses the place of their exhibition? These are some questions, and dozens of others, which interest me for thirty years in the field of exclusively urban works, that I will try to address , succinctly, here.