The 11 essays in this collection combine to present a broad overview of recent work on emotion conceived as a response that is both regulatory and regulated. Starting with a survey of fundamental conceptual issues, the discussion shifts to detailing the major biological systems involved in emotion regulation, and then moves to focus on relationships as a significant source of regulation. Contributors to Section 1 include: J. Kagan on the nature of emotion; R. Thompson on the multiple definitions of emotion regulation; S. Calkins on the origins of individual differences; and P. Cole et al. on clinical perspectives of emotional dysregulation. Section 2 features: K. Stansbury and M. Gunnar on adrenocortical activity; G. Dawson on individual differences recorded by EEG; N. Fox on dynamic cerebral processes; and S. Porges et al. on the role of the vagal system. In Section 3, the hidden biological regulators of early relationships are discussed by M. Hofer, the effects of maternal unavailability by T. Field, and the relation between quality of attachment and emotion regulation strategies by J. Cassidy.