Institutions shape many of the things people do. Th ink of waiting in line in a store, giving way to a car coming from the right (or left , depending on where you are), ordering a meal in a restaurant, buying a house, getting married, chairing a meeting, and running a multi-billion corporation. Th ere are two perspectives on what examples such as these have in common in both philosophy and the social sciences. According to the fi rst, each is an instance of a particular kind of behavioral regularity or recurring activity. According to the second, each is an instance of a certain kind of rule-based behavior. Th ese two perspectives are sometimes combined (Aoki 2011;Greif and Kingston 2011;Hindriks and Guala 2015). In this vein, Raimo Tuomela (2013) argues that institutions are normgoverned social practices. As social practices are recurring activities and as norms are rules, this defi nition-on which I will rely in this chapter-captures both perspectives.Institutional actions are caused by intentional attitudes. Oft en those attitudes are taken to be individual beliefs and desires-or, in the language of rational choice theory, expectations and preferences. I might, for instance, have a preference to drive on the right hand side of the road given that everybody else drives on this side. My decision to drive on this side of the road, on this type of analysis, is based in part on what I take your beliefs and desires to be, as well as on mutual beliefs about such attitudes. Your attitudes feature as parameters in my decision process and vice versa. In light of each other's attitudes, we mutually adjust our behavior to each other. Th is form of interdependence is commonly referred to as "strategic interaction. "Alternatively, institutional actions might involve a stronger form of interdependence in that they are based on collective attitudes instead. Collective intentional states involve a "we" as their subject instead of merely two or more I's. As a consequence, a collective attitude such as a belief or intention will be conceived of as "our" attitude, our belief or intention. Parties to a collective attitude take each other's agency more seriously than agents whose attitudes are regarded merely as parameters in strategic interaction. As I discuss in Section 1, diff erent theories of collective intentionality spell this out in diff erent terms.