This chapter presents the new 5G radio interface and the principles in the functioning of the 5G radio network. It describes some of the most relevant theories and technologies related to 5G. Then, the chapter gives an overview of the 5G spectrum, including discussion of the feasibility of wider bandwidth utilization in theory and practice, planned 5G radio frequency bandwidths and band allocations, as well as the latest news and expectations of the World Radio Conference of the radio section of International Telecommunication Union (ITU-R) as the forum establishes the foundation of the global utilization and rules of the 5G radio frequencies. Next, the 5G Radio Access Technologies (RATs) are discussed with an explanation of the principles of established and further expected technologies, advanced multiple-in, multiple-out, and carrier aggregation. The chapter includes discussion of the ITU-R RAT candidates, proposed 3GPP design, and how it addresses the ITU-R Recommendations and use cases for 5G.