Researchers at the Whitehead Institute and The Sanger Centre report their contributions to the methodology and progress of The SNP Consortium, an international effort to assemble and release the first high-resolution map of common variations in human DNA called single nucleotide polymorphisms, or SNPs. SNPs are the bedrock of human genetics: they can be used to track inheritance of any gene, contribute to the traits that make us unique, and underlie our susceptibilities to common diseases such as cancer, diabetes, and heart disease. It is also believed that SNPs help explain why individuals respond differently to drugs.