This new book presents the results of a study of the evolutionary history and classification of living birds based on comparisons on comparisons of the DNAs (genetic material) of about 1700 species. Sibley and Ahlquist’s “DNA-DNA hybridization” technique is a biochemical method that measures the degree of genetic similarity between the DNAs of different species. This method has been applied to studies of other groups of organisms, but this book includes the largest set of DNA comparisons for any group. The book includes an introduction to the structure and function of DNA, the regulation of genetic information, the factors that determine the rate and extent of the reassociation of DNA fragments and the thermal stability of double-stranded DNA, the organization of the genomes of birds and other organisms, the families of repeated DNA, comparative DNA studies, the technique of DNA hybridization, and the methods used for comparative studies of DNA reassociation and dissociation. Other topics include the tempo of molecular evolution, methods of data analysis, and the factors that affect the rate of genomic evolution. The sections concerned with the phylogeny and classification of birds provide a chronological survey of the classification of birds since Linnaeus (1758) and details for each group of birds since that time. The history of the classification of each order and family is reviewed morphological characters are noted, and evidence of the phylogeny and genetic relationships of each group is given. With 385 figures of DNA melting curves and phylogenetic trees, plus an extensive bibliography, this book is a valuable resource for ornithologists and other biologists.