This chapter on marital satisfaction begins with the historical origins of such research. The first major section of the chapter reviews research on marital satisfaction, starting with five key features of this research (e.g., using self-report measures, largely non-theoretical) and then provides findings in multiple domains: behavior, cognition, and emotion. A middle section distinguishes two approaches: (a) an interpersonal approach that typically looks at patterns of interaction (e.g., communication, companionship, conflict), and tends to use terms such as adjustment and (b) an intrapersonal approach that focuses on individual judgments, namely subjective evaluations of relationships, and tends to use such terms as satisfaction and happiness. At the operational level, much of the past research has used measures lacking precision developed on the basis of classical test theory. Item Response Theory (IRT) analysis is now being used to develop relationship satisfaction measures. Instead of seeing marital satisfaction as a bipolar, unidimensional construct with a positive and negative end on the same continuum, the authors argue the field will advance by using a two-dimensional conceptualization and measurement approach: the experience of positive and negative affect are substantively distinct yet related phenomena, best assessed separately. The chapter concludes with seven issues needing to be resolved.