We analyze the mutual relations among firms’ capital structure, ownership structure, and valuation. Through the estimation of a system of simultaneous equations for a sample of 1,130 firms from 16 countries from both the common law and the civil law environments, our results confirm the differential effect of ownership structure on firms’ value in each setting. Whereas in civil law firms the higher ownership concentration results in an entrenchment and an alignment effect, in the common law firms higher ownership concentration increases the value of the firm. Second, we corroborate the endogeneity of ownership structure since we find that ownership structure is affected by the value of the firm and by the capital structure. Third, our results suggest that corporate finance decisions are taken simultaneously with other mechanisms of corporate governance and conditional on firms’ valuation.