This white paper introduces the concepts of virtual radio access networks (vRANs) and open RAN and explains how these new approaches to building mobile networks are transforming the ways service providers design, build, operate, optimize, and maintain their mobile networks, particularly their radio access networks. It presents the key benefits service providers can expect from the adoption of virtual RAN or open RAN, which include flexibility, scalability, agility, innovation, vendor diversity, lower cost of ownership, and simplicity of operations.