JGroups is a toolkit for reliable group communication. Processes can join a group, send messages to all members or single members, and receive messages from members in the group. The system keeps track of the members in every group, and notifies group members when a new member joins, or an existing member leaves or crashes. A group is identified by its name. Groups do not have to be created explicitly; when a process joins a non-existing group, that group will be created automatically. Member processes of a group can be located on the same host, within the same LAN, or across a WAN. A member can be part of multiple groups.