CoAP is a RESTful transfer protocol for constrained devices and networks. It is anticipated that constrained devices will often naturally operate in groups (e.g. in a building automation scenario all lights in a given room may need to be switched on/off as a group). This document provides guidance for how the CoAP protocol should be used in a group communication context. An approach for using CoAP on top of IP multicast is detailed for both constrained and un-constrained networks. Also, various use cases and corresponding protocol flows are provided to illustrate important concepts. Finally, guidance is provided for deployment in various network topologies.