Legal positivism lacks a comprehensive theory of legal obligation. Hart's account of legal obligation, if successful, would explain only how the rule of recognition obligates officials. There is nothing in Hart's account of social obligation and social norms that would explain how the legal norms that govern citizen behavior give rise to legal obligations. However, we cannot give a theoretical explanation of the concept of legal obligation without a theoretical explanation of the concept of obligation. If legal, social and moral obligations are three instances of the kind defined by “obligation,” then we cannot successfully explicate the nature of legal, social or moral obligations without a successful general conceptual theory of obligation. In what follows, I attempt to develop what I take to be the central elements of the general concept of obligation. I argue that obligations are (1) associated with mandatory prescriptions; (2) reasons for action; (3) exclusionary in the sense that certain reasons are excluded as an excuse of justification for non-performance; and (4) “binding” in the sense that they have a special normative force. At the end of the paper, I briefly argue that our shared concept of obligation is indeterminate with respect to one theoretically important case, the issue of whether the rules of a crime gang that includes some sort of rule-defining procedures for making rules governing members obligate gang members if accepted as legitimate by the members.