Motivated by the unprecedented levels of economic policy uncertainty (EPU) recently experienced in Europe, we study how EPU affects capital structure and whether cultural, institutional, and financial conditions and corporate diversification moderate this relationship in a sample of 3175 firms from eleven European countries. Firstly, our results indicate that financial leverage is positively related to EPU, with this relationship being moderated by uncertainty avoidance, institutional quality, and financial development. Secondly, corporate debt is positively related to corporate diversification. This relationship is stronger for unrelated than for related diversification. In addition to the direct effect, both types of diversification indirectly moderate the positive influence of EPU on leverage, with this effect being stronger for unrelated diversification. Our results show that debt and uncertainty avoidance, institutional quality, and financial development work as substitute mechanisms to alleviate the agency costs caused by EPU and that corporate diversification reduces the informational gap between firm insiders and outside investors exacerbated by EPU.