The Collaborative Study of Obesity and Diabetes in Adults (CODA) project was formed to establish an international database of studies of abdominal obesity and type 2 diabetes mellitus (T2DM), and to provide analyses of these associations using individual participant data (IPD) meta-analytic techniques. The collaboration involves obtaining raw data from existing studies. The main objectives of the collaboration are to assess which simple anthropometric indices most closely predict the risk of T2DM in adults, and to investigate ethnicity and other factors that potentially modify that prediction. A second task related to primary prevention of diabetes subsequently evolved, the CODA-2 project, and is concerned with population-based methods to identify people most likely to benefit from diabetes interventions. This article describes the meta-analysis design and the studies involved. The collaboration currently has 37 studies enrolled, providing data on 260 000 participants. The proposed IPD meta-analyses will help resolve several outstanding issues in diabetes.