This volume examines a variety of empirical strands to construct an overall view of how young peers behave with each other. The substantive material derives from an interweaving of two sources: a critical survey of reported findings, of the methods that were used in establishing them and of their relationship to the conclusions that have been offered; and the writer's own longitudinal study of development during the second year of life. This study not only provides an empirical evaluation of the plausibility of existing hypotheses, it synthesizes widely diverse findings and methods into a comprehensive picture of current trends and new directions in toddler-peer research.