The HapMap Web site at http://www.hapmap.org is the primary portal to genotype data produced as part of the International Haplotype Map Project. In phase I of the project, >1.1 million SNPs were genotyped in 270 individuals from four worldwide populations. The HapMap Web site provides researchers with a number of tools that allow them to analyze the data as well as download data for local analyses. This paper presents step-by-step guides to using those tools, including guides for retrieving genotype and frequency data, picking tag-SNPs for use in association studies, viewing haplotypes graphically, and examining marker-to-marker LD patterns.