The term “collective action” is hopelessly broad. Taken at face value, it could plausibly refer to all forms of human behavior involving two or more people. Suffice it to say, consideration of such a broadly inclusive category would be well beyond the scope of this entry. But there is a far narrower subset of human action, to which the term has been applied and which will be the focus here. For our purposes, collective action will refer to emergent and at least minimally co-ordinated action by two or more people that is motivated by a desire to change some aspect of social life or to resist changes proposed by others. By “emergent” I mean innovative lines of action that depart from taken-for-granted normative routines. “Co-ordinated” simply means that the various parties to the emerging action are attuned to, and acting in awareness of, each other. Finally, the emphasis on change or resistance to change is intended to capture the adversarial or potentially contentious nature of “collective action.”