This chapter focuses on Mobile GIS (MGIS), which uses wireless networks and small screen mobile devices (such as PDAs and smartphones) to collect or deliver real time, location specific information and services. Such services can be divided into field and consumer (location based services) GIS applications. The use of wireless networks and small screen devices, introduce a series of challenges, not faced by desktop or wired internet GIS applications. This chapter discusses the challenges faced by mobile GIS (e.g. small screen, bandwidth, positioning accuracy, interoperability, etc.) and the various means of overcoming these problems, including the rapid advances in relevant technologies. Despite the challenges, many efficient and effective Mobile GIS applications have been developed, offering a glimpse of the potential market.