What is distinctive about the study of collective intentionality within the broader study of social interactions and structures is its focus on the conceptual and psychological features of joint or shared actions and attitudes, and their implications for the nature of social groups and their functioning. This Handbook fully captures this distinctive nature of the field and how it subsumes the study of collective action, responsibility, reasoning, thought, intention, emotion, phenomenology, decision-making, knowledge, trust, rationality, cooperation, competition, and related issues, as well as how these underpin social practices, organizations, conventions, institutions and social ontology. Like the field, the Handbook is interdisciplinary, drawing on research in philosophy, cognitive science, linguistics, legal theory, anthropology, sociology, computer science, psychology, economics, and political science. Finally, the Handbook promotes several specific goals: (1) it provides an important resource for students and researchers interested in collective intentionality; (2) it integrates work across disciplines and areas of research as it helps to define the shape and scope of an emerging area of research; (3) it advances the study of collective intentionality.