In the past decade, there has been a dramatic growth in research examining the development of emotion from a physiological perspective. However, this widespread use of physiological measures to study emotional development coexists with relatively few guiding principles, thus reducing opportunities to move the field forward in innovative ways. The goal of this monograph is to present the state of the science on the physiology of emotion from a developmental perspective in order to take stock of the knowledge base at this historical moment in time and to cultivate greater integration and coordination in the field as a whole.