The International HapMap Project's website (http://www.hapmap.org) is the primary portal for genotype data generated by the project. The site provides tools for data analysis, retrieval, and download. The paper describes these tools and their use in studying genetic variation and association studies. The project aims to map common genetic diversity in the human genome to accelerate the search for genetic causes of disease. In phase I, over 1.1 million SNPs were genotyped in 270 individuals from four populations. Phase II includes genotyping 4.6 million SNPs. The data are available for public use, with over 500,000 downloads and 30,000 monthly page requests. The site is organized into three main sections: Home, About the Project, and Data. The Data section offers bulk downloads, interactive browsing, and analysis tools. The site also includes a genome browser for visualizing SNP distribution and patterns of common variation. Additional tools include HapMart for data mining and a tag-SNP picker for association studies. The site also allows downloading genotyping data in formats suitable for analysis. Future developments include integrating with other genome browsers and providing tools for uploading and analyzing genetic association data. The HapMap website is a resource for visualizing, retrieving, and analyzing high-throughput, high-quality genome-wide human genetic data, supporting disease association studies. It is currently in development and provides basic tools for visualizing common polymorphism patterns, selecting tag-SNPs, and generating customized data extracts. The site will evolve to offer more services for genetic association studies in the future.The International HapMap Project's website (http://www.hapmap.org) is the primary portal for genotype data generated by the project. The site provides tools for data analysis, retrieval, and download. The paper describes these tools and their use in studying genetic variation and association studies. The project aims to map common genetic diversity in the human genome to accelerate the search for genetic causes of disease. In phase I, over 1.1 million SNPs were genotyped in 270 individuals from four populations. Phase II includes genotyping 4.6 million SNPs. The data are available for public use, with over 500,000 downloads and 30,000 monthly page requests. The site is organized into three main sections: Home, About the Project, and Data. The Data section offers bulk downloads, interactive browsing, and analysis tools. The site also includes a genome browser for visualizing SNP distribution and patterns of common variation. Additional tools include HapMart for data mining and a tag-SNP picker for association studies. The site also allows downloading genotyping data in formats suitable for analysis. Future developments include integrating with other genome browsers and providing tools for uploading and analyzing genetic association data. The HapMap website is a resource for visualizing, retrieving, and analyzing high-throughput, high-quality genome-wide human genetic data, supporting disease association studies. It is currently in development and provides basic tools for visualizing common polymorphism patterns, selecting tag-SNPs, and generating customized data extracts. The site will evolve to offer more services for genetic association studies in the future.