This chapter provides detailed insights into drivers and motivations for the new 5G System. It gives an overview of the System and radio access network (RAN) Architecture, architectural requirements, basic principles of the new architecture and the role of technology enablers in developing this new architecture. It provides a comparison with evolved packet system (EPS), describes the essence of the 5G System, newly introduced features and explains how interworking between EPS and 5G System will work in detail. This chapter also provides a detailed description of the key 5G System features including network slicing, data storage principles for improved network resiliency and information exposure, generic exposure framework, architectural enablers for mobile edge computing, support for 3rd Generation Partnership Project (3GPP) access and non-3GPP access, fixed-mobile convergence, support for internet protocol multimedia subsystem (IMS), short message service (SMS), location services, public warning system, policy and charging. It also includes a summary of the control and user plane protocol stacks used in the 5G System.