A host group is a set of zero or more hosts. When a message is sent, it is delivered to all members of the host group identified by the address of the message. Internet Protocol(IP) Multicast is implemented on the Internet and it supports host group. It has no multicast address management mechanism such as address allocation, and two different host groups can have the same address at the same time. Messages within a group may disrupt the operation of the other group. The host group management system coordinates the use of multicast address and helps programmers to develop multiuesr applications easily. The system consists of the group address manager, the group address binder, the group manager, and the host group management library. We show a sample application; shared editor built using the host group management library.