Modern gene-mapping can include linkage studies, which correlate the presence of disease to broad genomic regions in either small or large family units, and association studies, which can narrow the location of a disease-predisposing trait to a single gene using either case-control or family data. This unit provides an overview of key concepts and presents guidelines for collecting diagnostic, epidemiological, and genealogical data from potential study participants. The commentary discusses the use of publicly available data from online resources, methods for evaluating evidence of genetic versus environmental influences in a disease or disease-related endophenotype, and use of e-forms to capture data electronically.