Chapter by Claire Borsenberger, Mathilde Hoang and Denis Joram: “Thanks to appropriate data algorithms, firms, especially those on-line, are able to extract detailed knowledge about consumers and markets. This raises the question of the essential facility character of data. Moreover, the features of digital markets lead to a concentration of this core input in the hands of few big “superstars” and arouse legitimate economic and societal concerns. In a more and more data-driven society, one could ask if data openness is a solution to deal with power derived from data concentration. We conclude that only a case-by-case approach should be followed. Mandatory open data policy should be conditioned on an ex-ante cost-benefit analysis proving that the benefits of disclosure exceed its costs….(More)”.