Given that they are responsible for much of the meaning that we attribute to our existence, emotions could be said to have a central role in the psychological life of humans. But given this fundamental level of significance, the construct of emotion remains poorly understood, with the field of emotion research being full of conflicting definitions and opposing theoretical perspectives. In this review, one particular aspect of research into emotion is considered: the development of emotion in infancy and early childhood. The development of the emotional life of the child has been the focus of a vast amount of research and theorizing, so in a brief review it is only possible to scratch the surface of this topic. Rather than any attempt at a comprehensive account, three perennial questions in theorizing and research on early emotional development will be considered. First, what develops in emotional development? Second, what is the relation of cognitive development to emotional development? Third, how has the study of early individual differences in emotion expression typically been approached? In relation to the first question, four theoretical approaches to emotional development are described. For the second question, the focus is on the relation of self-awareness to the development of emotion. Finally, for the third question, the use of temperament theory as a framework for understanding individual differences in emotion expression is examined. Copyright © 2010 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs website.