Although it was first published twenty years ago, Stuart Pimm's Food Webs remains the clearest introduction yet to the study of food webs, diagrams depicting which species interact - in other words, who eats whom. Reviewing various hypotheses in light of theoretical and empirical evidence, Pimm shows that even the most complex food webs follow certain patterns, and that those patterns are shaped by a limited number of biological processes - processes he provides mathematical tools for unraveling (and concrete examples of those tools' application). This edition adds a new foreword covering recent developments in the study of food webs and demonstrating their continuing importance to conservation biology, particularly attempts to predict which communities are most vulnerable to disturbance.