Multicast is a set of technologies that enables efficient delivery of data to many locations on a network. Network multicast capability is crucial for a variety of applications, including distance learning, digital video libraries, and online collaboration tools. Internet2’s non-commercial research and education networks have made the speedy deployment of multicast possible. Through the work of Internet2’s industry partners, and of standards bodies such as the Internet Engineering Task Force, the technologies being tested in the Internet2 multicast effort are now making their way into the global Internet. A new Internet2 Multicast publication further describes the advantages of multicast over unicast technology.