Interpersonal power involves how much actors can influence partners (actor power) and how much partners can influence actors (partner power). Yet, most theories and investigations of power conflate the effects of actor and partner power, creating a fundamental ambiguity in the literature regarding how power shapes social behavior. We demonstrate that actor and partner power are distinct and have differential effects on social behavior. Six studies (total N = 1,787) tested whether actor and partner power independently predicted behavioral inhibition (expressive suppression) and communal behavior (prioritization of partners' needs) within close relationships, including during couples' daily life (Study 1), lab-based social interactions (Studies 1-5; 1,012 dyadic interactions), and general responses during conflict (Studies 5 and 6). Actor power was negatively associated with behavioral inhibition, indicating that actors' low power prompts self-focused inhibition to prevent negative outcomes that low power actors are unable to control. Partner power was positively associated with actors' communal behavior, indicating that high partner power prompts other-focused behavior that prioritizes partners' needs and goals. These differential effects of actor and partner power replicated in work-based relationships with bosses/managers (Study 6). Unexpectedly, partner power was negatively associated with actors' behavioral inhibition within close relationships, consistent with a desire to prevent negative outcomes for low power partners. We present a framework that integrates the approach-inhibition and agentic-communal theories of power to account for the differential effects of actor and partner power. We describe the implications of this framework for understanding the effects of power in both close and hierarchical relationships. (PsycInfo Database Record (c) 2023 APA, all rights reserved).