In the public domain, the artistic expression embodies different forms which go from the most ›intellectual‹ and respondent to what one can see in the ›world of art‹ (installations, performances, videos etc.) to the most popular or alternative ones, like graffiti and flash mobs. 1 They all stem from esthetical, political and ethical projects. It would be impossible to account for all of them in the urban space, unless we follow Paul Ardenne's idea of contextual art, that is of unauthorised as well as legitimate actions implying the physical valorisation of the public sphere: »With ›contextual‹ art we mean all the forms of art which differ from the work of art as it is understood traditionally, such as: militant and committed activist art (happenings in the public space, artistic movements etc.); art taking place in the public domain or in its landscape (street performances, situational landscape art...), and the forms of esthetical participation in the fields of economy, media or show business.« (Ardenne 2002: 11) Even if it were possible to index the artistic work exposed in the public space, beyond its diversity, one could only note the common theme of its specific context, at the margins of the artistic world, therein sharing the limitations characteristic of such a context. Thus, to exhibit in this domain, which is shared by everybody and governed by social rules (social and juridical norms, rights and obligations meant to guarantee public welfare, security and order), necessarily changes the relationship to the audience. The visitor/member of the public does no longer move within an exhibition space, which is delimited by a specific physical area and framed by the conventions of the artistic world 2 , but does so in a public space, with all its implications. 1 This text-including all the citations, in French-was translated by Dafne Accoroni. 2 One can notice that a number of rules are shared by different domains in the social world, together with others which may add to these. Among the constraints cited above are those which can alter the reception of the artistic work in the urban space, such as noise, traffic, advertising or random reactions.