Launched in 2002, the International HapMap Project was a collaborative effort among scientists from around the world to create a map of common patterns of genetic variation in the human genome. HapMap stands for haplotype map. A haplotype is a stretch of DNA nucleotides, or letters, that individuals inherit as a block because they lie relatively close together along a chromosome. For any particular region of a chromosome, there may be multiple different haplotypes present among humans, each characterized by a slightly different DNA sequence. By collecting and sequencing the DNA of initially 270 individuals from several different geographic regions, HapMap scientists were able to identify common haplotypes that exist among those individuals, as well as reliable markers to distinguish them. That collection of haplotypes and identifying markers—the HapMap—provided a shortcut for researchers who wanted to identify associations between those inherited DNA variants and particular human traits, especially common, complex diseases like heart disease and cancer.

A genome-wide association study, or GWAS, is a method for identifying variations in DNA that may contribute to the development of a particular trait, such as a disease. A GWAS relies on identifying statistical correlations between many, often thousands of, DNA markers and a particular trait. Scientists employ GWASs to try to identify the genetic contributions to complex traits, such as common human diseases. Complex traits are ones that scientists suspect are the result of multiple genes and environmental inputs acting together, in contrast to simple, Mendelian disorders that result primarily from the disturbance of a single gene. The genetic variants identified through a GWAS typically account for only a small proportion of the expected genetic contribution to a complex trait, which scientists refer to as the missing heritability problem. Since 2006, scientists have conducted thousands of GWASs aimed at identifying the genetic contributions to complex traits and have identified many thousands of genetic variations that correlate with those traits, although as of 2025, because of the missing heritability problem and other limitations, the concrete contributions of GWASs to medicine have so far been modest.