Philosophers and scientists have long debated the nature of human social interactions and the prevalence of mutual dependence, conflict of interests, and power asymmetry in social situations. Yet, there is surprisingly little empirical work documenting the patterns of interdependence that people experience in daily life. We use experience sampling to study how people think about 3 dimensions of interdependence in daily life and how these dimensions relate to cooperation. In Study 1, 139 romantic couples (n = 278) reported on situations experienced with their partner (k = 6,766); in Study 2, individuals (n = 284) reported on situations experienced with any other person (k = 7,248), over the course of 1 week. Across both samples, we found that most social interactions were perceived as containing moderate mutual dependence, equal power, and corresponding interests. When couples reported on the same situation (Study 1), they largely agreed on their experienced interdependence and cooperation, suggesting that their reports reflect an underlying shared reality. In daily interactions across both samples, higher mutual dependence and lower conflict of interests were associated with more cooperation, whereas relative power was not directly related to cooperation. These associations replicated in laboratory experiments (Study 2). In daily life, high mutual dependence and high relative power exacerbated the negative relation between conflict of interests and cooperation. Finally, prevalent patterns of interdependence and the experience of specific interdependent situations affected multiple relationship outcomes. Our findings stress the importance of studying a diverse array of interdependent situations—and especially situations with corresponding interests—to better understand cooperation in daily life. (PsycInfo Database Record (c) 2021 APA, all rights reserved)