This chapter summarizes technical requirements for 5G systems as per the 3rd Generation Partnership Project (3GPP) Release 16 and the International Telecommunications Union (ITU) International Mobile Telecommunications 2020 (IMT-2020). 5GC and NR form the 5G System (5GS). It enhances capacity and performance, and complies with the demanding requirements for eMBB, mMTC, and URLLC. eMBB, mMTC, and URLLC are the elemental building blocks, or dimensions, of 5G as indicated in the ITU IMT-2020, which sets the reference for the new era. The NGMN is an initiative that also contributes, among many other technology areas, to 5G development. In a parallel fashion with the standardization work of 5G, several mobile network operators have been testing and developing concepts for 5G. These activities have helped understand the performance of the NR and core network concepts and has eased the evaluation work of the standardization bodies.