Wireless technologies have expanded greatly over the past few years as a result of numerous technological advances and regulatory changes. Although rail and urban transit operators have long used radio systems primarily for voice communications, they are increasingly deploying new wireless networks in support of advanced applications for themselves and their customers. These applications have the potential to streamline rail and transit operations, enhance customers' travel experience, and act as a new source of revenue. This paper reviews the recent technological advances and regulatory changes that have encouraged the proliferation of mobile wireless devices and networks and examines the issues associated with their design and deployment in the rail and urban transit environment.