The fifth generation (5G) mobile network is a new generation of wireless systems that is intended to connect users faster and more reliable than any previous generation. Mobile operators are adopting new radio access technologies that can provide service anywhere and through any interface of connectivity. The 5G networks will employ massive cloud storage to facilitate their computational operations. The 5G requirements reflect the end-user requirements and the upper band availability in both spectrum and technology. The continuous developments in the massive MIMO and beamforming techniques allow accessing the millimeter wave spectrum to support ultradense high-capacity scenarios. The chapter also presents an overview of this book. The book divides the 5G challenges into five parts to investigate: physical layer for 5G radio interface technologies, radio access technology for 5G networks, 5G network interworking and core network advancements, vertical 5G applications, and R&D and 5G standardization.