This chapter reviews scholarship on marital well-being, focusing on the affective dynamics within marriage. It provides a conceptual overview of the literature and suggests directions that may lead to a better understanding of how and why marriages change. Specifically, the chapter describes the emotional climate of marriage, arguing that it is crucial to examine both positive and negative affect in marriage, separately and in combination. The chapter also describes a model of the emotional climate of a marriage with two core constructs: affection and antagonism. Next, the chapter discusses the importance of taking a developmental perspective of marriage, and then reviews and critiques various theoretical models of how marriages change, including (a) the emergent distress model, (b) the disillusionment model, (c) the enduring dynamics model, and (d) accommodation models. The chapter also examines factors that influence why marriages change in particular ways, such as courtship, characteristics of spouses, and life events. The chapter concludes with recommendations that future work on marriage focus greater attention on (a) diversity in marriage, (b) multiple aspects of affect, and (c) the varied pathways toward dissatisfaction and/or divorce.