This chapter reviews how the 5G technology is a key element in the development of sustainable smart cities. It details the major features of 5G, which include ultra-low latency, massive IoT connectivity, energy efficiency, among others, and how they will affect infrastructure, transportation, general safety, urban environment controls in cities. Allowing more efficient, quicker and scalable urban systems, 5G becomes a backbone of smarter, greener and more resilient cities of tomorrow.