There has been a data revolution: the combination of sensors, processing power and mobile communications means that there is more of it, and it is having a greater impact on our lives than ever before. Across the world, there have recently been many new initiatives and legislative proposals for opening up access to some of that data. This is often driven by two different motivations: the desire to create new positive outcomes with existing resources, and the desire to correct negative impacts on competition in markets. To regulate data access properly, it is necessary to understand what makes data different and what its value is. If data access is going to be mandated, how can one value the data that a business holds, and set fair and reasonable charges for access to it? Economic tools that analyse the cost of creating the data, and the benefits derived from it, provide critical insight into this question.