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ulticasting is growing in importance as new applications are devised. Throughout this article, multicasting is understood as the efficient multipoint-to-multipoint transmission of information (in terms of network resource consumption) between the members of a group. In particular, the focus is on the problems of deploying the multicast service in an ATM environment. ATM has been widely deployed in current networks. However, such networks do not allow the efficient provisioning of multipoint-to-multipoint communications. This lack of efficiency occurs because current solutions seek to reproduce a connectionless environment over ATM, which is connectionoriented. For connectionless environments, the applications developed using the TCP/IP protocol suite are mostly oriented to work over broadcast networks. The connectionless nature of IP makes broadcast networks a natural choice. In these networks, multicast forwarding is carried out very easily. A multicast packet with a group address is sent over the broadcast network and is only delivered to those hosts that have joined the group. This characteristic is not present in connection-oriented networks (e.g., ATM), where the sender must establish a connection with all group members before packets can be forwarded. On the other hand, native approaches offer the multicast facility at the ATM level, and they therefore take its connection-oriented nature into account. Apart from this conceptual difference, ATM introduces further challenges to the multicasting problem due to quality of service (QoS) provisioning issues. All these unsolved problems make ATM multicasting a challenging field. These aspects are discussed in the following subsections.