Genetic epidemiology is the study of the role of genes and environments on markers of health and disease risk in populations. It emerged as a mainstream discipline in the early 1980s, arising from firm foundations laid by mathematical population genetics, clinical genetics, and statistical epidemiology. Though genetic epidemiology attempts to identify the many components of risk attributable to genes, environments, and interactions between these two factors, the course of the research towards this goal can follow many diverse paths. In the last few years, the success of genome-wide association studies in their identification of hundreds of disease susceptibility loci has brought this specialist field to the forefront of biomedical research. Advances in molecular genetics will soon offer affordable means to measure or observe study participant's genetic material at the sequence level as well as more detailed functional data, such as gene expression.