In the present chapter, we advance a reciprocal influence model of social power. Our model is rooted in evolutionist analyses of primate hierarchies, and notions that the capacity for subordinates to form alliances imposes important demands upon those in power, and that power heuristically reduces the likelihood of conflicts within groups. Guided by these assumptions, we posit a set of propositions regarding the reciprocal nature of power, and review recent supporting data. With respect to the acquisition of social power, we show that power is afforded to those individuals and strategic behaviors related to advancing the interests of the group. With respect to constraints upon power, we detail how group-based representations (a fellow group member's reputation), communication (gossip), and self-assessments (an individual's modest sense of power) constrain the actions of those in power according to how they advance group interests. Finally, with respect to the notion that power acts as a social interaction heuristic, we examine how social power is readily and accurately perceived by group members and gives priority to the emotions, goals, and actions of high-power individuals in shaping interdependent action. We conclude with a discussion of recent studies of the subjective sense of power and class-based ideologies.