Foreword The papers in these proceedings were presented at the 39th Annual Symposium on Foundations of Computer Science (FOCS ‘98), sponsored by the IEEE Computer Society Technical Committee on Mathematical Foundations of Computing. The conference was held in Palo Alto, California, November g-11,1998. The program committee consisted of Miklos Ajtai (IBM Almaden), Mihir Bellare (UC San Diego), Allan Borodin (Toronto), Edith Cohen (AT&T Labs), Sally Goldman (Washington), David Karger (MIT), Jon Kleinberg (Cornell), Rajeev Motwani (chair, Stanford)), Seffi Naor (Technion), Christos Papadimitriou (Berkeley), Toni Pitassi (Arizona), Dan Spielman (MIT), Eli Upfal (Brown), Emo Welzl (ETH Zurich), David Williamson (IBM TJ Watson), and Frances Yao (Xerox PARC). The program committee met on June 26-28, 1998, and selected 76 papers from the 204 detailed abstracts submitted. The submissions were not refereed, and many of them represent reports of continuing research. It is expected that most of these papers will appear in a more complete and polished form in scientific journals in the future. The program committee selected two papers to jointly receive the Machtey Award for the best student-authored paper. These two papers were: “A Factor 2 Approximation Algorithm for the Generalized Steiner Network Problem” by Kamal Jain, and “The Shortest Vector in a Lattice is Hard to Approximate to within Some Constant” by Daniele Micciancio. There were many excellent candidates for this award, each one deserving. At this conference we organized, for the first time, a set of three tutorials: “Geometric Computation and the Art of Sampling” by Jiri Matousek; “Theoretical Issues in Probabilistic Artificial Intelligence” by Michael Kearns; and, “Information Retrieval on the Web” by Andrei Broder and Monika Henzinger. The committee wishes to thank all those who submitted papers for consideration, as well as those who helped with the process of evaluating the submissions. A list of the latter individuals appears in these proceedings under the heading “Reviewers.” The program committee chair also wishes to thank David Karger and Joe Kilian for help with the electronic submission server, Kristine Kelly for serving as an editor of these proceedings, and especially Alok Aggarwal, Anna Karlin, and Prabhakar Raghavan for advice and assistance. Special thanks to Michael Mitzenmacher for hosting the committee meeting and for a wonderful job of organizing the entire conference. Rajeev Motwani Program Committee Chair xi.