This monograph reports on a 14 month study of yellow baboons (Papio cynocephalus) in the Masai-Amboseli Game Reserve, Kenya. The study was an attempt to determine the relationship between agonistic dominance and reproductive success in male baboons and centered around testing a priority-of-access model of mating behavior. Explicit criteria for determining dominance in baboons are presented and the consistency of dominance relationships through time is analyzed for all classes of individuals. Related data on reproductive cycle length, perineal and behavioral indications of the optimal day for mating, changes in female behavior during estrus, and effects of the presence of estrous females on group organization are also included. This work constitutes the first comprehensive field study of baboon mating systems and social organization and emphasizes the use of systematic behavior sampling techniques in the field and quantitative models in the study of primate social behavior.