Encyclopedia article. The article offers a philosophical and sociological analysis of the concept of power. The author starts from an intuitively reliable definition, according to which power is an asymmetric and stable social relation. Characterization of power as a relation dismisses its substantial definition as a quality, ability or force. The substantial definition turns out to be ineffective in the theoretical perspective because power implies correlation of forces and not simply force. The relation between two agents does not fully describes the power relation since one of the parties is usually backed by superior resources. This fact indicates a stable asymmetry inherent in power. However, this asymmetry is not absolute in its nature: power as a social relation persists only if subordinate party has a relative freedom of action. Thus, the time horizon of power is established: the asymmetry of forces during a power struggle turns into asymmetry during the end of this struggle, which forms, in case of preservation and consolidation of second asymmetry, a third asymmetry that is stable power. The spatial horizon of power is formed not by the bodies of agents but by actions, which are expected within the framework of the relationship. These actions in their turn presuppose motivations. As the social differentiation grows and the communication network becomes more complicated, it would be difficult to understand the motivations of the parties. We might treat the concept of power in many alternative ways: either as a necessary component of social life or as disguised coercion; either as a universal or a specific relation; either as a purely individual relation or as a feature of the relations of different communities; either as an effect achieved in spite of resistance or as an opportunity to achieve an effect enhanced by solidarity. The article concludes with a brief overview of contemporary definitions of power, provided by social theory (M. Weber’s classical definition, post-Parsonian concepts of power by R. Dahl, M. Mann, N. Luhmann and S. Lukes) and political philosophy (H. Arendt).