What determines states’ ability to influence the contents of international institutions? Extant scholarship on international economic negotiations highlights the importance of political and economic capacity in negotiations. In this article, we argue that another structural source of negotiating power has been overlooked: bureaucratic capacity. Building on in-depth interviews with a large sample of international economic negotiators, we develop a theory of how differences in bureaucratic capacity can give states advantages in bilateral negotiations. We test our theory on a dataset of bilateral investment treaties. To measure preference attainment, we combine a unique repository of states’ public negotiating mandates called model treaties and the texts of finalized investment treaties to compute the verbatim distances between states’ stated preferences and the treaties they negotiate. We then show that states with greater bureaucratic capacity than their counterparts tend to achieve higher preference attainment in investment treaty negotiations. Our results have important implications for scholarship on international negotiations and for policy-makers engaged in investment policy reform.