Social interaction is crucial for understanding individual and collective processes in knowledge communities. We describe how technology has changed the way people interact in large communities. Building on this description, we propose a framework that distinguishes four types of joint interactions in online knowledge communities: Attendance, Coordination, Cooperation, and Collaboration (A[subscript 3]C framework). These four types of interactions vary depending on the extent to which community members share their goals, processes, and outcomes. Attendance, the weakest form of joint interaction, is characterized by individualistic orientations; people may belong to a community but are still driven by individualistic goals, work as individuals, and produce outcomes for personal benefits. Coordination, a stronger form of interaction, is characterized by interdependence among community members; members still act largely as individuals, but their goals, processes, and outcomes are now interdependent or contingent on other community members. Cooperation is characterized by shared goals and outcomes, but the process of achieving the goal is not fully shared; members coordinate their activities and may also engage in some joint processes but work individually for most of the time. Collaboration is characterized by sharing in all of the dimensions involved; people share the processes, as well as the goals and outcomes of their work. These four types of joint interactions are not mutually exclusive, but instead build on each other. We discuss how the A[subscript 3]C framework may serve as a guide for future research and can support design efforts in online knowledge communities.