San Diego County, in southernmost California, boasts the largest number of species for any county or area of comparable size in the United States—almost 500, more than most states. Commensurate with this large total comes this heavy tome, packed with information and looking more like the avifaunal work for some states than for a “mere county.” As well as a large avifauna, San Diego County lays claim to a burgeoning human population which, as Unitt notes, combines third-world growth rates with first-world consumption rates. The inevitable result is increasing pressure on all habitats throughout the county. The production of the San Diego County Atlas (hereafter Atlas) coincided with the development of a multiple-species conservation plan for metropolitan San Diego and similar plans for other parts of the county. Thus, the Atlas offers a timely benchmark from which the efficacy of such plans can be evaluated, as well as an exhaustive model of how a regional avifaunal work should be approached.