Many scholars primarily view international organizations as vehicles used by powerful states to distribute resources. However, this view trivializes the profound influence of their day-to-day operations on the world. This dissertation argues that that the classification systems developed by these bureaucracies significantly affect how classified countries are treated by many influential elites in the global economy. Focusing on the domain of development, I show that whether a country is categorized as a developing country has major effects on high-stakes decisions such as aid, investment, and credit and democracy ratings. Why do international observers rely so heavily on these blunt categories? I propose two mechanisms by which classifications influence elite behavior: Elites may use classifications cognitively as heuristic devices that simplify decision-making processes or strategically as a way of justifying their behaviors to external audiences. I then show with cross-national data from 1987 to 2015 that a country's World Bank income classification correlates with the rewards it receives from actors who are susceptible to one or both of these mechanisms. Specifically, I find that becoming a middle income country causes a country to lose aid but receive better ratings of its creditworthiness and democracy. These findings are echoed in interviews with stakeholders in the graduation processes of several countries within a World Bank system. I test the micro-foundations of my theory with experimental data by inviting an elite sample of development professionals and students to participate in a hypothetical aid allocation activity. By randomizing the information included on the country profiles and the participation incentives, I show both that a classification effect exists and that, in the case of donors, it is primarily driven by the strategic mechanism. Coupled with the observational findings, which illustrate that classifications affect investors and raters with no such strategic incentives, this suggests that both mechanisms are essential to understanding who uses classifications. How do these dynamics affect the experiences and behaviors of classified countries and groups within those countries? I argue that classifications produce winners and losers, who strategically respond to their classifications when able and informed. In particular, being categorized as a more developed country punishes non-governmental organizations and those they represent, while business interests and individual leaders benefit materially and socially. I illustrate these patterns through dozens of interviews with representatives from civil society, the business community, and government in Nepal and Botswana, two countries that are currently or have previously "graduated" from the UN's Least Developed Country category. Moreover, I provide qualitative and quantitative evidence that countries use a variety of strategies to attempt to change their classifications, and they do so in both directions. For example, I show that countries manipulate their data as they approach significant thresholds that separate categories, and while some seek to accelerate their transition, others try to hinder it. This project identifies and explains a relatively unexamined power of international organizations in a context where its deployment significantly affects outcomes for developing countries. Classifications affect the highest level of interactions in ways that are felt by the poorest in society. As numerous countries begin to graduate from their developing country statuses, these findings are especially relevant for ongoing policy debates about how international organizations spread their understandings of development. Far from merely describing the world, these bureaucrats shape it in profound ways.