This document describes best current practices that community administrators should use when interconnecting two or more instant messaging and presence communities using SIP/SIMPLE. These best practices are intended to assist in the efficiency and scalability of interconnections between large communities, and to ensure that security and user privacy are maintained across the link between communities. The purpose of this document is to serve as the reference for the SIP/SIMPLE community towards inter-domain interoperability and also to identify new requirements specific to the inter-domain interface.