Part I Introduction.- The Values and Challenges of Long-Term Field Studies.- Part II Madagascar.- Berenty Reserve, Madagascar: A Long Time in a Small Space.- Beza Mahafaly Special Reserve: Long-Term Research on Lemurs in Southwestern Madagascar.- Long-Term Lemur Research at Centre Valbio, Ranomafana National Park, Madagascar.- A 15-Year Perspective on the Social Organization and Life History of Sifaka in Kirindy Forest.- Part III America.- The Northern Muriqui (Brachyteles hypoxanthus): Lessons on Behavioral Plasticity and Population Dynamics from a Critically Endangered Species.- The Lomas Barbudal Monkey Project: Two Decades of Research on Cebus capucinus.- Tracking Neotropical Monkeys in Santa Rosa: Lessons from a Regenerating Costa Rican Dry Forest.- The Group Life Cycle and Demography of Brown Capuchin Monkeys (Cebus [apella] nigritus) in Iguazú National Park, Argentina.- Part IV Asia.- Social Organization and Male Residence Pattern in Phayre's Leaf Monkeys.- White-Handed Gibbons of Khao Yai: Social Flexibility, Complex Reproductive Strategies, and a Slow Life History.- V Africa.- The Amboseli Baboon Research Project: Forty Years of Continuity and Change.- The Thirty Year Blues: What We Know and Don't Know About Life History, Group Size, and Group Fission of Blue Monkeys in the Kakamega Forest, Kenya.- Long-Term Research on Chimpanzee Behavioral Ecology in Kibale National Park, Uganda.- Long-Term Field Studies of Chimpanzees at Mahale Mountains National Park, Tanzania.- Long-Term Studies of the Chimpanzees of Gombe National Park, Tanzania.- Long-Term Research on Grauer's Gorillas in Kahuzi-Biega National Park, DRC: Life History, Foraging Strategies, and Ecological Differentiation from Sympatric Chimpanzees.- Long-Term Studies on Wild Bonobos at Wamba, Luo Scientific Reserve, D.R. Congo: Towards the Understanding of Female Life History in a Male-Philopatric Species. VI Summary.- A Comparative Perspective on Long-term Field Studies.