The objective of this document is to address the Inter-IMS Network to Network Interface (II-NNI) consisting of Ici and Izi reference points between IMS networks in order to support end-to-end service interoperability. The present document will address the issues related to control plane signalling (3GPP usage of SIP and SDP protocols, required SIP headers) as well as other interconnecting aspects like security, numbering/naming/addressing and user plane issues as transport protocol, media and codecs actually covered in a widespread set of 3GPP specifications. Charging aspects will be addressed as far as SIP signalling is concerned. The purpose of this document is to prepare some material that could be moved to the foreseen Technical Specification for the profiling of the Inter-IMS Network to Network Interface (II-NNI) and to propose if any needed modifications of the 3GPP core specifications are required.