The rise of the online economy is based on the opportunities to extract value from data that is produced by digital technologies. As opposed to data brokers that gain value buying and selling personal information, this report argues for radically new ideas about how the value of our personal information can be returned back to citizens. Rather than focusing on how making money from data, it focuses on how data can benefit society as a whole, exploring the idea of ‘data commons’. The report is entitled “Common Knowledge: Citizen-led data governance for better cities” and is part of the decode H2020 project.