Law is a social construction. The fundamentally social character of normative facts in the legal domain implies that a legal order is the consequence of a complex interaction of reciprocal forces between norms and human activities. This thesis argues against the prevailing view that characterizes law’s normative significance as giving independent reasons for action and provides a more comprehensive account of the social facts underlying a legal system, on the basis of which the role of law in providing normative guidance for its addressees can be unfolded. The argument develops by virtue of amplifying the role of power-conferring norms in explaining the core official legal practices, the efficacy of law, the social basis of law, the authority structure of law, and the reason-giving force of law respectively. One’s committed attitude toward an empowering norm is the practical attitude that shows one’s recognition of the normative consequences that ensue from exercises of the legal power conferred by that norm. The social basis of law consists primarily in exercises of legal powers that connect formal laws with informal social customs and integrate them into the overall normative order within a jurisdiction. The authority of law is a de facto authority, the existence of which depends on a social context in which the legal agents’ recognition of their roles within the authority structure is manifested in their exercises of legal powers. Law provides two modes of normative guidance: the directive mode and the constitutive mode. These two modes of guidance jointly constitute the distinctive manner in which law performs the action-guiding function. The normative significance of legal authority is manifested in its ability to render modes of conduct proper responses to pre-existing reasons. Legal power plays a pivotal role in the operations of law. It is the vital nexus of the sociality of law, the normativity of law, and the authority of law. Exercise of legal powers not only manifests the dynamics and agility of law, but also secures the stability and systematic coherence of a legal order. The exercise of legal power is the core of legal practices as a rational activity of human beings – our ability to be engaged in rule-following activities that establish normative order.