This chapter discusses the early development of mastery in infancy in the light of a new life-span model of primary and secondary control. It explores the functional significance of mastery motivation for effective action regulation is discussed from a phylogenetic and ontogenetic viewpoint. The functional significance of early onset preferences for behaviour event contingencies lies in their potential to activate the organism, enhance the salience and direct attention towards potentially effective behaviour, and thus promote the acquisition of mastery. Social interactions with caretakers play a key role in the early development of human mastery. The chapter argues that this holds not only with regard to the social facilitation of behaviour event contingency experiences, but also with respect to the evolution of action regulation and self-evaluative reactions to success and failure. In early infancy, behaviour event contingencies can be experienced only in interactions with social partners who provide contingent reactions to the infant's behaviour.