No metric more strongly illustrates global health than the vast series of numbers gathered in the Global Burden of Disease (GBD), a massive health data collection enterprise currently run and made available by the Institute for Health Metrics and Evaluation (IHME) at the University of Seattle with the financial support of the Gates Foundation. This system for assessing the impact of disease encompasses quite different numbers than those circulating in public health circles, such as epidemiological results or clinical trials outcomes. Looking at the trajectory of the GBD through reports, archives, interviews with actors from the World Bank, the WHO, networks centered on particular health conditions, or national and sub-national health administrations, this chapter tells a story about the economic turn in world health and the health turn in the economics of development. This story contrasts two periods. The first one covers the construction of this metric through a combination of health data and an external economic calculus involved in the World Bank’s “health turn,” a shift from massive infrastructural development projects to human capital investments like health and education in the 1990s. The chapter then examines the disjunction between how the GBD was conceptualized, with a strong focus on the comparative evaluation of cost-effectiveness, and how it was actually applied in global health policy. After some dormancy, the GBD reappeared, from the mid-2000s, as an enterprise of the university-affiliated IHME Institute on Health Metrics and Evaluation (IHME). In the hands of think tanks, consulting firms, governments, NGOs, academics, and the WHO, the GBD has moved from development economics to the health arenas of low- and middle-income countries (LMIC). Through this journey it has lost its edge as determining tool in health policies with the consequence that global health priorities worldwide and comparative burden data are barely related. GBD today has become a shared language whose numbers are reworked at the national level, used in isolation, as indicators of emergency, as developments in mental health or medical genetics show.