This encyclopedic global survey of leguminous root nodulation, the result of 45 years of research by O. N. Allen and Ethel K. Allen, is the only one of its kind, a massive effort incorporating all of the 750 known genera of Leguminosae, which, in turn, include nearly 20,000 species. The volume contains a comprehensive taxonomic account of the family Leguminosae as a framework for the author’s census report of the nodulating and non-nodulating genera and species. The main body of the work consists of synopses of 750 leguminous genera arranged alphabetically. Each is described taxonomically within its proper tribe and subfamily, in accordance with accepted classification systems. All of the nodulation data from the survey are further summarized in tabular alphabetical listings of genera under each of the three subfamily categories. Throughout the volume there are previously unpublished personal observations, both those of the authors and of the many scientists whom they have contacted and worked with during their more than four decades of research.