The invention provides a method and system for content-based filtering of multicast information. A set of sources (S) which desire to distribute potentially large numbers of categories of differing information each associates a content descriptor (CD) with messages including information in those categories, so that a set of recipients (R) can receive information in at least some of those categories. A mapping server (M) associates a multicast address (MA) and a content mask (CM) with each content descriptor, so that network elements (N), such as routers, in the network can distribute only those messages which are of interest to recipients in multicast distribution trees for those multicast addresses. Each source generates content descriptors for each differentiable topic in a tree structured hierarchy, and obtains a multicast address and a content mask for the broadest content descriptor it is capable of distributing. Each recipient obtains the associated source, multicast address, and content mask, for each content descriptor of interest, and uses that information to join the multicast distribution tree for that information. Each network element between the source and the recipient determines what information it must forward for further distribution in response to the content descriptors, content masks, multicast addresses, and multicast distribution trees.