In today’s highly dynamic and interactive business environment, the role of “customer engagement” (CE) in cocreating customer experience and value is receiving increasing attention from business practitioners and academics alike. Despite this interest, systematic scholarly inquiry into the concept and its conceptual distinctiveness from other, associated relational concepts has been limited to date. This article explores the theoretical foundations of CE by drawing on relationship marketing theory and the service-dominant (S-D) logic. The analysis also examines the use of the term “engagement” in the social science, management, and marketing academic literatures, as well as in specific business practice applications. Five fundamental propositions (FPs) derived from this analysis are used to develop a general definition of CE, and distinguish the concept from other relational concepts, including “participation” and “involvement.” The five propositions are used in the development of a framework for future research, the undertaking of which would facilitate the subsequent refinement of the conceptual domain of CE. Overall, CE, based on its relational foundations of interactive experience and the cocreation of value, is shown to represent an important concept for research in marketing and service management.