This book serves three purposes. First, it is one of the five permanent records that are outcomes of the Fourth International Conference on Integrating Geographic Information Systems (GIS) and Environmental Modeling (GIS/EM4), held in Banff, Canada in September 2000. The other four permanent records are the research record of the meeting: special issues of theJournal of Environmental Management(Clarke et al., 2000a) andTransactions in GIS(Clarke et al, 2000b), plus the CD-ROM Proceedings for the meeting (Parks et al., 2001), and the permanent conference Web site ( http://www.colorado.edu/research/cires/banff/ ). This book is different from the research results from the meeting in a fundamental way, since it is designed with the second purpose in mind, that of education. The book is intended for use in the advanced classroom or seminar to introduce students to the power that GIS offers to computer-based models of the environment. This education purpose is critical, because the editors of this volume believe that the decade of work on integrating GIS and environmental modeling has now yielded fruit, and the benefits will be reaped by a new generation of authors with much work ahead of them. Third, the book is an opportunity for a set of scholars, most of whom attended GIS/EM4, to establish where the state of the art lies at the turn on the century, after a productive first decade. In retrospect, it seems astonishing that when GIS/EM1 was held, there was no World Wide Web, GIS was still largely command-line driven stand-alone computer programs, and practical data interoperability was merely a pipedream. The key word in the conference name, not reflected in this book's abbreviated title, isintegration.The selection of sites in the Rocky Mountain region for the GIS/EM conferences over the years, Boulder, Breckenridge, Santa Fe, and Banff, was deliberate. It symbolized the divide between the two adjacent fields of environmental modeling and GIS. Environmental models, regardless of disciplinary specialization, shared a mathematical and statistical core, an algorithmic arid a methodological periphery, and common concerns of application, model effectiveness, calibration and validation, computational implementation, and utility. Geographic information systems combined methods and functions yet faced immense practical and theoretical barriers as they gained use as ubiquitous tools for the management, display, and analysis of spatial data. At the surface there was a common boundary at the divide based on needs: for data, for visualization of pattern, and for objective scientific problem solving. GIS brought the bright light of complex reality to the elegant but blemished face of simplified mathematical models. It was an uneasy meeting at first, but throughout the 1990s the crispness of the divide line became fuzzy, and the separate sciences became integrated in their quest to explain the world and its systems, rather than advocate a single discipline as holding the solutions. The GIS/EM4 visual used with permission for the conference and on the cover of this book, Escher's "Puddle," is an excellent metaphor for this transformed science. In a single glimpse, Escher integrates clouds and weather, trees and soil, rain and surface water. And yet this integrated view shows these physical phenomena by indirect refection, instead directing the viewer toward human impacts upon these "natural" environmental elements. Footsteps, vehicle tracks, and puddles hint at an unseen environmental modifier, homo sapiens. The scene makes sense only in unity, viewed through the puddle, just as the environment yields to simulation only by integrating knowledge. The image of trees seen via a puddle in tire tracks is inverted and geometrically distorted, of course. Equally transformed is the environment, seen in isolation through the eyes of a single scientific diClarke, Keith C. is the author of 'Geographic Information Systems and Environmental Modeling' with ISBN 9780130408174 and ISBN 0130408174.