This study provides factual evidence on potential issues related to access and (re-)use of data in platform-to-business relations. Based on interviews with online platforms and businesses, a survey of businesses, and a literature review, the study identifies the different categories of data generated through online platforms and assesses a) the extent of access and (re-)use possibilities granted by platforms at present, b) the value placed by businesses on such access and (re-)use and c) the impact of a potential change in platform practices regarding data access and (re-)use. The study finds that business users generally do not have access to some data which they value highly for marketing purposes, in particular customer email addresses, information on platform user profiles, and user behaviour data. Enhanced access to data could have a significant impact on businesses’ turnover though this is conditional on business knowledge of and experience with data analysis. Finally, the study examines two sets of policy options: 1) Requiring greater transparency on data access and use policies towards business users, and 2) Mandating access to certain categories of data. While the first option does not raise any particular legal concern, and has the advantage of addressing businesses’ lack of awareness as regards data and its possible uses, the second option must be designed in conformity with the requirements of the GDPR. Furthermore, this option would in parallel have to address the lack of awareness of business users as regards data in order to be fully effective in its potential impacts..