Book excerpt: This volume presents a systematic philosophical theory related to the collectivism-versus-individualism debate in the social sciences. A weak version of collectivism (the "we-mode" approach) that depends on group-based collective intentionality is developed in the book. We-mode collective intentionality is not individualistically reducible and is needed to complement individualistic accounts in social scientific theorizing. The we-mode approach is used in the book to account for collective intention and action, cooperation, group attitudes, social practices and institutions as well as group solidarity.