This work provides information for approximately 2850 American scientists deceased through 1920. It utilizes standard published biographical sources (biographical directories, dictionaries, and indexes), as well as obituary and similar notices for some persons not in standard sources. Arranged alphabetically by personal name, the Biographical Index includes full name, year of birth and death, scientific field(s) in which the person was active, identification by occupational category, reference to unpublished material described in the National Union Catalog of Manuscript Collections, and references to published biographical sources. All fields of science are covered, including mathematics, astronomy, physics, chemistry, geology, the biological sciences, psychology and anthropology, as well as some persons noted for contributions in engineering, invention, and medicine. An index of the scientists by scientific field appears at the end of the work. Beyond its primary value as a reference tool for the location of information on particular persons, the Biographical Index also serves to identify the population of scientists in America who lived during the period from colonial times to 1920. Selection of names was based on a systematic review of certain works such as the Dictionary of American Biography and other specialized indexes such as E.S. Barr's Index to Biographical Fragments in Unspecialized Scientific Journals, obituary notices in American journals indexed in the Royal Society's Catalogue of Scientific Papers (1867-1925), lists of deceased scientists in American Men of Science, and other sources. While eminent scientists are included, a number of less notable personages also arelisted. This bibliography is suitable for college and research libraries and public libraries of all sizes, and for individuals interested in the history of American science.