In this paper, we examine the intra- and interindividual variability of daily affect in adult couples. We use a variety of analytic techniques to inspect the daily fluctuations in emotions and to determine whether such fluctuations are influenced by the partner’s affect as well as the weather. The techniques include multiple regression analysis, longitudinal mixed models, and differential equations. To illustrate the different approaches, we use data consisting of self-reports of affect from ten adult couples that filled out a questionnaire daily for three months. All analytic approaches include parameters representing effects from the couple (i.e., oneself and partner) and from external sources (i.e., daily temperature).