A key goal of biomedical science is to understand why individuals differ in their susceptibility to disease. Family history is among the established risk factors for most forms of cardiovascular disease, in part because inherited DNA sequence variants play a causal role in disease susceptibility. Consequently, the search for these variants has intensified over the past decade. One class of DNA sequence variants takes the form of single nucleotide changes(single nucleotide polymorphisms, or SNPs), usually with two variants or alleles for each SNP. SNPs are scattered throughout the 23 pairs of chromosomes of the human genome, and roughly 11 million common polymorphisms (ie,those > 1% frequency) are estimated to exist. A combination of SNP alleles along a chromosome is termed a haplotype. The International Haplotype Map Project was designed to create a public genome-wide database of common SNPs and, consequently, enable systematic studies of most common SNPs for their potential role in human disease. We review the following: (1) the concept of linkage disequilibrium orallelic association, (2) the HapMap project, and (3) several examples of the utility of HapMap data in genetic mapping for cardiovascular disease phenotypes.