Technology and policy are coming together to enable a paradigmatic change to the most widely used mechanism, exclusive rights, which allows mobile telecommunications operators to use the radio spectrum. Although spectrum sharing is not a new idea, the limited supply of spectrum and the enormous demand for mobile broadband services are forcing spectrum authorities to look more closely into a range of tools that might accelerate its adoption. This paper seeks to understand how co-existence and co-operation of Wi-Fi and cellular networks in the unlicensed spectrum can increase the overall capacity of heterogeneous wireless networks. It also reveals the challenges posed by new uses, such as machine-to-machine communications and the Internet of Things. It also brings together two major proposed regulatory approaches, such as those by the U.K.'s Ofcom and the European Commission, which currently represent leading efforts to provide spectrum authorities with robust spectrum sharing frameworks, to discuss policy tools likely to be implemented.