These contributions from six leading laboratories document experimentally established findings about mental representations in animals and the role these representations play in the genesis of behavior. Animal representations in a number of widely different domains are analyzed - time and number in rats, space in foraging bees, conditioning events in rats, stimulus categorization in pigeons, and social structure in vervet monkeys - in order to determine whether animals have behaviorally consequential representations of their environment that can tell us about mind in general. In his introduction, Gallistel defines the controversial concept of representation as having the same meaning in psychology as it has in mathematics - a formal correspondence, or isomorphism, between two systems that makes it possible to use operations in one system to draw conclusions about the other. The modern experimental work reported here seeks to derive from animal behavioral data the mental representations or processes in the brain isomorphic to specific aspects of the animal"s environment that function to adapt its behavior to that environment. C. R. Gallistel is Professor of Psychology at University of California, Los Angeles. Contents: Representations in Animal Cognition: An Introduction, C. R. Gallistel. Representation of Time, John Gibbon, Russell M. Church. Alternative Representations of Time, Number, and Rate, Russell M. Church, Hilary A. Broadbent. Honey Bee Cognition, James L. Gould. Event Representation in Pavlovian Conditioning: Image and Action, Peter C. Holland. Levels of Stimulus Control: A Functional Approach, R. J. Herrnstein. The Representation of Social Relations by Monkeys, Dorothy L. Cheney, Robert M. Seyfarth.