We would like to thank Jeff Huang and Michael Smith, who participated in the field project described in this chapter. We also thank Martha Broad and John Quimby for their help. Parts of this chapter appeared previously in Malone et al. (1999) and Bernstein et al. (1999). The work was supported, in part, by the National Science Foundation (Grant Nos. IRI-8903034, IRI-9224093, and DMI-9628949) and the Defense Advanced Research Projects Agency (DARPA). It was also supported by the following corporate sponsors: British Telecom, Daimler Benz, Digital Equipment Corporation, Electronic Data Systems (EDS), Fuji Xerox, Matsushita, National Westminster Bank, Statoil, Telia, Union Bank of Switzerland, Unilever, and other sponsors of the MIT Center for Coordination Science and the MIT Initiative on ''Inventing the Organizations of the 21st Century.''The software described in this paper is the subject of the following patents owned by MIT and licensed to Phios Corporation: US Patent Nos. 5,819,270 and 6,070,163; European Patent No. 0692113.