The past decade has seen a steady increase in studies oflemur behavior and ecology. As a result, there is much novel information on newly studied populations, and even newly discovered species, that has not yet been published or summarized. In fact, lemurs have not been the focus of an international symposium since the Prosimian Biology Conference in London in 1972. Moreover, research on lemurs has reached a new quality by addressing general issues in behavioral ecology and evolutionary biology. Although lemurs provide important comparative information on these topics, this aspect of research on lemurs has not been reviewed and compared with similar studies in other primate radiations. Thus, as did many in the field, we felt that the time was ripe to review and synthesize our knowledge of lemur behavioral ecology. Following an initiative by Gerry Doyle, we organized a symposium at the XIVth Congress of the International Primatological Society in Strasbourg, France, where 15 contributions summarized much new information on lemur social systems and their ecological basis. This volume provides a collection of the papers presented at the Strasbourg symposium (plus two reports from recently completed field projects). Each chapter was peer-reviewed, typically by one "lemurologist" and one other biologist. The first three chapters present novel information from the first long-term field studies of three enigmatic species. Sterling describes the social organization of Daubentonia madagascariensis, showing that aye-aye ranging patterns deviate from those of all other nocturnal primates.