This paper assesses the regulation of smartphone 'app stores'. At the outset, the adoption of smartphones and apps is noted, alongside the ways in which scholars and journalists have used these markets as the basis for the discussion of legal and economic issues. The importance (commercially and as a study in governance and control) of the iOS App Store (Apple) is highlighted. Part 2 deals with the relationship between Apple and app developers; three themes of Apple's Guidelines are identified (content, development and payments), and the ways in which control can be challenged (through jailbreaking, 'web apps' and regulatory intervention) are scrutinised. Part 3 considers three ways in which apps are already regulated by law: the protection of consumers (particularly through the UK system for 'premium rate services'), user privacy, and (in brief) the regulation of video games and video-ondemand services in Europe. Finally, in part 4, the tension between comparatively 'open' and 'closed' app stores is highlighted; the problems of applying general provisions to emerging formats are emphasised. It is concluded that the emerging status of non-carrier app stores as neither retailer nor platform means that it is not yet possible to identify the form of regulation that is in operation, but that some steps are