An enthusiastic tour of cyberspace by one of its pioneers. In Virtual Reality (1991), Rheingold explored one corner of the amazing new world created and accessed by computers; here, in an equally well-informed but even more messianic (and cautionary) survey, he reports on ``the Net,'' the ``loosely interconnected computer networks...that link people around the world into public discussions.'' Like a physical net, the Net contains myriad knots, or loci: Rheingold's home locus is the Well, a San Francisco-based network that he's been logging on to since 1985 for about 14 hours a week in order to ``talk,'' via modem, to hundreds of people in assorted ``conferences.'' To Rheingold, the Well is a paradigm of computer networking--decentralized, informal, eclectic, and self- governing, a ``virtual community'' in which people meet, collaborate, argue, even fall in love, but all without physical contact--and he devotes much space to its power and wonder (when one member of the Well's Parenting conference announced that his son had contracted leukemia, for instance, other members responded on-line with overwhelming emotional and informational support). Rheingold covers the haphazard history of the Net, not missing the irony of its roots in a Defense Department project (though here his discussion gets relatively technical and acronym-packed), and he examines how it operates overseas, particularly in Japan and France (where the government-sponsored network is dominated by sex ``chat''). Despite his conviction that the Net represents grass- roots ``groupmind'' in action, Rheingold recognizes its dark side- -most dramatically, in the popular ``Multi-User Dungeons'' in which networkers indulge in elaborate--and highly addictive--role-playing fantasies; and in the very real possibility that governments and megacorporations will eventually misuse the Net as a way to spy, or to download products, on a logged-on public. Rheingold's central point is that there's a revolution taking place on-line; with this thoughtful, supportive critique, he's continuing his fair bid to be its Tom Paine.