Why do people stay in a personal relationship? For decades, scholars have attempted to answer this deceptively simple question. In doing so, they have often invoked the concept of commitment. Relationship commitment is a core construct within relationship science, and theorizing and research on it, including its antecedents and consequences, has been active for years. This chapter reviews what is known currently about commitment processes, including why it remains a particularly important construct in understanding relationships today. We begin by providing basic conceptualizations offered for the construct, highlighting why the construct seems of importance given shifts in how people relate with one another at the current time. We then review particularly generative extant theoretical models of commitment (including the Cohesiveness Model, the Tripartite Model, and the Investment Model of Commitment Processes), before turning to a detailed review of known antecedents of commitment. We also review known consequences of commitment (including cognitive, affective and behavioral consequences). We end the chapter by considering topics for potential future exploration.