On January 2, 1957, at the Apollinaire Gallery in Milan, Yves Klein inaugurates the exhibition of eleven perfectly identical blue monochromes, which, he claims later, are then displayed and sold at different prices. Who, however, of the artist or the market, is the most arbitrary in awarding prizes? Two reflections will intertwine: one, theoretical, on the case study that Klein gives us in the valuation and evaluation of a multiple work of art, in the light of the economic thought on the value ; the other, more historical, will examine the destiny reserved by the market for these serial works.