t be clear yet what applications will be served by 5G networks, the demand for 5G is there and mobile networks, RAN in particular, need to evolve to cope with such traffic in a cost- and energy-efficient manner. Increased throughputs and new spectrum (e.g. mmWave) are not the only, and maybe not even the primary, 5G driving factors. Additional drivers are cost and energy efficiency con- siderations, competition (between operators, vendors, and even market sectors and tech- nologies), and even politics, in what is sometimes referred to as the "race to 5G." In this chapter we elaborate on the various forces driving 5G technology development and deployment with emphasis on how these impact RAN features, RAN-related technologies, and RAN architecture, which is the primary focus of the book. Key Ideas Data traffic in general and mobile traffic in particular is expected to continue growing exponentially. In the past, spectrum needs forecasts significantly underestimated actual data usage. To alleviate this issue, the ITU Radiocommunication Sector (ITU-R) used a new approach that forecasts spectrum needs ranging from hundreds of MHz to tens of GHz. The 5G tar- get spectrum consists of lower frequency ranges (below 1 GHz), middle frequency ranges (below 6 GHz), and higher frequency ranges (mmWave) to cater to different applications. As the 5G spectrum is expected to be an order of magnitude larger than 4G, this will have a direct impact on RAN. Spectrum-sharing models, such as Citizens Broadband Radio Service (CBRS) in the USA and Licensed Shared Access (LSA) in Europe, may further increase available spectrum. 2 Market Drivers Furthermore, they may trigger new RAN deployment options, such as the neutral host operator model. Even though CBRS and LSA are currently based on LTE, we expect that in the future spectrum-sharing models will become applicable to 5G as well. In order for a technology to qualify for IMT-2020, it must fulfill certain technical require- ments broadly categorized as: enhanced mobile broadband (eMBB), 