Thispaperstarts from thepremise thatat theRio+20Summit,historyhas repeateditselfand that the same expectations raised by bioprospecting 20 years ago are now attached to the market-based instruments associated with conservation policies (Payments for environmental services, REDD mechanisms, biodiversity offsets,...). The promise that market mechanisms are best suited to reach biodiversity conservation goals has been renewed. Building on Polanyian definition of fictitious commodities and on the idea of the ‘economy of promises’ (developed by P.B. Joly in relation to biotechnologies and nanotechnologies), we argue that beyond their ideological foundations, market mechanisms require complex institutional arrangements that are often irrelevant and ineffective in reaching theirenvironmental objectives.Thesevariousmarket-based ormarket-like arrangements rely onthereassertedpromiseofasynergybetweenmarketandconservationratherthanonactualmarket mechanisms. They are supposedly meant as conservation tools. However, they rather foster the developmentofamarketforconsultingandeconomicexpertiseinconservationissues,thegrowthand perpetuation of which depend on the renewal of this promise, in the form of changing institutional arrangementsandmechanisms.