Network sharing is a way for operators to share the heavy deployment costs for mobile networks, especially in the roll-out phase. In the current mobile telephony marketplace, functionality that enables various forms of network sharing is becoming more and more important. These aspects have not really been addressed before Release 6 in 3GPP UTRAN based access networks, before Release 8 in 3GPP E-UTRAN based access networks and before Release 10 in 3GPP GERAN based access networks, although there has been functionality that supports a very basic type of network sharing since the Release 5 versions of the 3GPP specifications. The present document covers the details of Network Sharing for GERAN, UTRAN and E-UTRAN. It shows how several core network operators can share one radio access network and details the impacts on the network architecture. All UEs shall comply with existing requirements, among them PLMN selection and system information reception. The present document also defines requirements for network-sharing supporting UEs.