Behavioural Mechanisms of Food Selection examines animals belonging to diverse trophic groups, from carnivores, herbivores, micro-algal grazers, to filter-feeders and detritus-feeders. In the past Optimal Foraging Theory has been applied to all these groups, but in different ways and in disci plines that rarely overlap. Here concepts and developments hitherto scattered in the literature are drawn together. This uniquely broad synthesis captures the state of the art in the study of diet selection and prescribes new objectives in theoretical development and research.