Radio-over-Fibre (RoF) is an optical communication technique based on the transmission of standard wireless radio signals though optical fibre in their native format. This technique is an enabling step in the deployment of dense fourth generation (4G) cellular and pico-cellular wireless networks. The optical fibre provides a huge bandwidth that can support a variety of wireless systems, regardless of their frequency bands, being protocol-transparent which is reflected in an great network flexibility. Radio-over-fibre techniques enables a high user capacity by frequency reuse, simplifies the network operation as the signals are distribute in their native format, and permits to transfer signal part of the processing power from the base station units to the central control station, thus reducing the overall deployment cost and complexity. The principles of radio-over-fibre are presented in this chapter, including the key transmission impairments and the expected performance. The main application scenarios are discussed. These include the backhaul of 4G or base-stations, addressing 4G and 3G compatibility issues, and distributed-antenna system (DAS). Finally, emerging applications like radio-over-fibre in beyond-3G scenarios and transmission of 60 GHz wireless are also described in this chapter.