Systems Analysis and Simulation in Ecology, Volume IV continues the organization begun in Volume III to document a meeting, Modeling and Analysis of Ecosystems, held at the University of Georgia on 1-3 March 1973. Several chapters are considerably expanded over their original concept, and several others are included which were not part of the symposium. The book is organized into five parts. Part I contains chapters on estuarine-marine ecosystems. Part II presents models of several terrestrial ecosystems. Part III has chapters devoted to human aspects of ecology. Part IV considers special problems of ecosystem modeling, namely linear versus nonlinear models, aggregation, and validation. Part V, the most extensive section, describes theory in ecosystem analysis. The book's chapters demonstrate the current scope of systems ecology-its past and present emphasis on parts and mechanisms in simulation modeling, and its movement toward systems analysis and new, more formal consideration of wholes in theory. They make clear that although the systems approach is young in ecology, it has substantially enriched the science both methodologically and conceptually.