We analyze how access to data affects competition and consumer surplus in a model where more data allows firms to offer products that are better targeted to consumer preferences and at the same time to price discriminate more effectively. We find that consumer surplus in a monopoly market is highest for an intermediate level of data access, while it is increasing in available data when firms compete. The effect of data on competition is asymmetric: Competition becomes fiercer if the more poorly informed firm gets better information, but softens when the better informed firm improves its information. Firm's preferred choice of information is an outcome where they are strongly differentiated by information quality. This preference limits the possibility to create an informational level playing field via data sharing or data brokers, and explains why total surplus may drop following entry. If an entrant can use data gathered in one market in another market, entry does not necessarily improve overall consumer surplus, since it enhances the entrant's ability to price discriminate in the other market.
