Interdependence is a fundamental characteristic of social interactions. Interdependence Theory states that 6 dimensions describe differences between social situations. Here we examine if these 6 dimensions describe how people think about their interdependence with others in a situation. We find that people (in situ and ex situ) can reliably differentiate situations according to 5, but not 6, dimensions of interdependence: (a) mutual dependence, (b) power, (c) conflict, (d) future interdependence, and (e) information certainty. This model offers a unique framework for understanding how people think about social situations compared to another recent model of situation construal (DIAMONDS). Furthermore, we examine factors that are theorized to shape perceptions of interdependence, such as situational cues (e.g., nonverbal behavior) and personality (e.g., HEXACO and Social Value Orientation). We also study the implications of subjective interdependence for emotions and cooperative behavior during social interactions. This model of subjective interdependence explains substantial variation in the emotions people experience in situations (i.e., happiness, sadness, anger, and disgust), and explains 24% of the variance in cooperation, above and beyond the DIAMONDS model. Throughout these studies, we develop and validate a multidimensional measure of subjective outcome interdependence that can be used in diverse situations and relationships-the Situational Interdependence Scale (SIS). We discuss how this model of interdependence can be used to better understand how people think about social situations encountered in close relationships, organizations, and society.