There is significant standards development work being done by various Standards Development Organizations (SDOs) relating to Next Generation Networks (NGN) for telecommunications. ATIS has adopted its Next Generation Network architecture based upon the concept of IP Multimedia Subsystem (IMS) being defined by 3GPP and 3GPP2. ATIS is in the process of refining and evolving this concept to adapt to the evolution of the telecommunications networks in North America. The evolution of emergency services networks must follow the path of this evolution to next generation networks if they are to benefit from the capabilities of next generation networks. This Technical Report uses the term Emergency Services Next Generation Network (ES-NGN) to define an emergency services architecture based upon the ATIS definition of NGN. This Technical Report identifies standards and standards activities that are relevant to the evolution of emergency services networks in the context of next generation telecommunications networks. In addition it identifies potential gaps where standards need to be developed in order to complete the definition of emergency services in next generation networks. The focus of this Technical Report is the interconnection between the ES-NGN and networks that originate emergency calls. It also discusses connectivity to PSAPs and legacy emergency services networks.