This publication provides basic descriptive information about the 100 largest school districts (ranked by student membership) in the United States and jurisdictions (Bureau of Indian Affairs, Department of Defense Schools, American Samoa, Guam, the Northern Marianas, Puerto Rico, and the Virgin Islands). Almost one in every four public-school students in this nation is served by one of these 100 districts. They are distinguished from the average school district by characteristics in addition to sheer size of membership, such as average and median school size, pupil/teacher ratios, number of high school graduates, number of pupils receiving special-education services, and minority enrollment as a proportion of total enrollment. Information about these characteristics is found in 18 "basic tables." For the purpose of establishing a meaningful context for the information on the 100 largest districts, four text tables precede the basic tables and provide national data and data on the 100 largest school districts. Appendix A list the 500 largest school districts with some identifying information and basic statistical data. Appendix B is an alphabetical list of the 500 districts and their rank by membership size. Appendix C provides a count of the number of largest districts represented by state. Appendix D provides data for the 1990-91 school year. (RT)