Family and twin studies indicate that a substantial fraction of susceptibility to type 1 diabetes is attributable to genetic factors. These and other epidemiologic studies also implicate environmental factors as important triggers. Although the specific environmental factors that contribute to immune-mediated diabetes remain unknown, several of the relevant genetic factors have been identified using two main approaches: genome-wide linkage analysis and candidate gene association studies. This article reviews the epidemiology of type 1 diabetes, the relative merits of linkage and association studies, and the results achieved so far using these two approaches. Prospects for the future of type 1 diabetes genetics research are considered.