This diary study examined daily fluctuation in marital lust over a 56-day period. The purposes of the study were to describe typical patterns of lust over time and to examine intrapersonal and interpersonal associations between relationship affect, relationship states, and marital lust. We also tested various daily moderational predictions. Four patterns of daily fluctuation in lust were identified. Typical patterns varied from almost no fluctuation to wide fluctuation over time. Our findings showed that daily affect was generally related to lust both within partners and between partners. Also, spouses relational states (closeness and equality of power) moderated several of these intrapersonal and interpersonal associations. In general, the affect-lust link was strengthened by closeness and equality of power, while the lust-lust link between spouses was often conditioned by both relationship affect and relational states. However, the role of negative affect toward spouses in interactions with other constructs was not as expected. We discuss possible explanations for the findings and implications for further research.