Standards are being developed to support multicasting over a TCP/IP network such as the Internet. These standards, IP Multicast and Mbone, will allow users to easily join multicast groups.

Note that multicasting refers to sending a message to a select group whereas broadcasting refers to sending a message to everyone connected to a network.

The terms multicast and narrowcast are often used interchangeably, although narrowcast usually refers to the business model whereas multicast refers to the actual technology used to transmit the data.

Compare with unicast and anycast.

Introduction to IP Multicast routing 
This paper, from 3Com, describes the benefits of multicasting, the Multicast Backbone (MBONE), Class D addressing, and the operation of the Internet Group Management Protocol (IGMP) and explores a number of different algorithms that may potentially be employed by multicast routing protocols.

Multicast Routing
This page, from Cisco Systems, describes design considerations for multipoint communications.