The authors introduce the Drosophila melanogaster Genetic Reference Panel (DGRP), a new community resource consisting of full genome sequences of inbred lines of fruitflies. Because the lines are derived from a single outbred population, they capture a large amount of natural variation and are therefore ideal for the fine genotype–phenotype mapping of quantitative traits. An analysis of 168 lines emphasizes the potential of the DGRP by highlighting patterns of genetic polymorphisms, by identifying sites of positive and negative selection and by locating variants that are associated with quantitative traits.