The sharing of public infrastructure, the exchange of small services, and the traditional “cup of sugar borrowed from the neighbor” are practices intrinsic to most urban agglomerations. In the digital age, these sharing initiatives are facilitated by online platforms such as Feastly, Peerby, and HomeExchange. These platforms allow city residents to share the idle capacity of some of their assets (e.g., clothing, tools, or a spare bedroom) with other residents living in close proximity to them, or with tourists looking for accommodation. While these practices can be justified by efficiency and sustainability concerns, some of them appear to be in conflict with longstanding regulations on local transportation, food safety, zoning, taxation, and short-term accommodation. This Article explores urban peer-to-peer sharing practices from a comparative perspective and discusses how a number of large cities in Europe, the United States, and Asia are currently addressing the regulatory challenges inherent to sharing platforms. We argue that cities should rethink their regulations in light of this new form of urban sharing. The legal literature has thus far conveyed an incomplete image of the sharing economy by focusing on controversial platforms such as Uber and their ongoing lawsuits. In this Article, we reestablish the historical, economic, and legal meaning of genuine “urban sharing.” First, this Article distinguishes between genuinely collaborative initiatives that promote the sharing of underutilized assets (e.g., spare guestrooms) and non-collaborative platforms that are not driven by sustainable consumption (e.g., Uber). Second, it provides an overview of the economic and geographic sharing potential of cities and discusses how outdated regulations might restrict it. Third, drawing on the experience of the so-called sharing cities (e.g., Seoul), it suggests a new legal framework for the regulation of genuine sharing practices. In this context, we argue that cities should, in some cases, experiment with the regulation of sustainable sharing initiatives in order to gather more information as to their benefits or risks, and, in other cases, engage in collaborative decision-making by negotiating the content of new legal provisions and policies with digital platforms.