ABSTRACT Research Question/Issue Research presents mixed findings on the relationship between board size and firm performance. Acknowledging that larger boards simultaneously offer increased resources and face heightened coordination demands, we propose that the ongoing ambiguity in this relationship stems from the context‐dependent nature of how larger boards balance these two opposing forces. This paper introduces a novel contingency framework comprising three firm‐level factors (board independence, type of performance, and ownership concentration) and three country‐level factors (legal origin, in‐group collectivism, and gender egalitarianism) that determine whether board size relates positively or negatively to firm performance. Research Findings/Insights We test the predictive value of our contingency framework in a meta‐analysis based on 346 studies across 110 countries. At the firm level, the impact of board size differs by performance type, showing a stronger negative association with market‐based performance, whereas board independence and ownership concentration do not play a significant moderating role. At the country level, we find positive moderating influences of common law origin and high in‐group collectivism, while gender egalitarianism shows no moderating effect. Theoretical/Academic Implications Our contextual framework reconciles divergent findings on the board size–firm performance relationship. Our results highlight the futility of a “one‐size‐fits‐all” approach. It offers a contextualized view on the resource–coordination balance that acknowledges the important role of country‐level contingencies therein. All in all, our findings highlight that contextually imposed coordination demands make it more difficult for larger boards to capitalize on their resources. Practitioner/Policy Implications Board size recommendations need to be tailored to contextual variables such as performance type, legal system, and sociocultural factors.