An accurate view of adaptive mutations is essential to evolutionary genetics, but their rarity makes them difficult to study. This can be partially overcome using the many tools of yeast genetics and the ability to study very large populations over many generations. Adaptation to laboratory environments has occurred primarily by chromosomal rearrangements, often involving retrotransposons and apparently selected for their effects on gene regulation. Estimated rates of adaptive mutation are on the order of 1 in 10(11) cell divisions. There remains great potential for the genomic study of variation within yeast species to contribute to our understanding of adaptive mutation.