The International HapMap Consortium has developed a public database of common genetic variations in the human genome, including over one million single nucleotide polymorphisms (SNPs) genotyped in 269 DNA samples from four populations. This resource, known as the HapMap, documents the structure of linkage disequilibrium (LD) and low haplotype diversity, highlighting recombination hotspots and their impact on SNP correlations. The HapMap is designed to guide genetic association studies, shed light on structural variation and recombination, and identify loci subject to natural selection during human evolution. The consortium's work has advanced the understanding of the role of inherited genetic variation in human diseases and paved the way for more efficient and informative genetic studies. The Phase I of the HapMap project genotyped at least one common SNP every 5 kb across the genome, with a minor allele frequency (MAF) of 0.05 or greater, and included ten 500 kb regions for detailed analysis. The data demonstrate a block-like structure of LD, with long-range haplotypes and discontinuous LD patterns influenced by recombination rates. The HapMap also provides insights into population differentiation and allele frequency distributions, which are crucial for understanding genetic variation and its implications for disease studies. The consortium's efforts have significantly enhanced the efficiency and power of genetic association studies by identifying tag SNPs that can serve as proxies for other SNPs, reducing the number of genotyping assays needed while maintaining or improving statistical power.The International HapMap Consortium has developed a public database of common genetic variations in the human genome, including over one million single nucleotide polymorphisms (SNPs) genotyped in 269 DNA samples from four populations. This resource, known as the HapMap, documents the structure of linkage disequilibrium (LD) and low haplotype diversity, highlighting recombination hotspots and their impact on SNP correlations. The HapMap is designed to guide genetic association studies, shed light on structural variation and recombination, and identify loci subject to natural selection during human evolution. The consortium's work has advanced the understanding of the role of inherited genetic variation in human diseases and paved the way for more efficient and informative genetic studies. The Phase I of the HapMap project genotyped at least one common SNP every 5 kb across the genome, with a minor allele frequency (MAF) of 0.05 or greater, and included ten 500 kb regions for detailed analysis. The data demonstrate a block-like structure of LD, with long-range haplotypes and discontinuous LD patterns influenced by recombination rates. The HapMap also provides insights into population differentiation and allele frequency distributions, which are crucial for understanding genetic variation and its implications for disease studies. The consortium's efforts have significantly enhanced the efficiency and power of genetic association studies by identifying tag SNPs that can serve as proxies for other SNPs, reducing the number of genotyping assays needed while maintaining or improving statistical power.