In December 2004, the National Academy of Sciences sponsored a colloquiumon "Systematics and the Origin of Species" to celebrate Ernst Mayr’s100th anniversary and to explore current knowledge concerning the originof species. In 1942, Ernst Mayr, one of the twentieth century’s greatestscientists, published Systematics and the Origin of Species, a seminal book ofthe modern theory of evolution, where he advanced the significance of populationvariation in the understanding of evolutionary process and the originof new species. Mayr formulated the transition from Linnaeus’s static speciesconcept to the dynamic species concept of the modern theory of evolutionand emphasized the species as a community of populations, the role ofreproductive isolation, and the ecological interactions between species. In addition to a preceding essay by Edward O. Wilson, this book includesthe 16 papers presented by distinguished evolutionists at the colloquium. The papers are organized into sections covering the origins of species barriers, the processes of species divergence, the nature of species, the meaningof "species, " and genomic approaches for understanding diversity and speciation.