This handbook introduces the reader to the National Longitudinal Surveys (NLS) research project and the various data sets that comprise the NLS. It is designed to assist readers in making an informed decision on whether the NLS is an appropriate data source for their research needs and to provide additional resources for those who desire more information. Chapter 1 provides information on the NLS, including the NLS samples, development of the NLS, purposes of the surveys, uses of the NLS, administration of the project, and current status and directions. Sections 2, 3, and 4 provide overviews of the NLS samples: the National Longitudinal Survey of Youth (NLSY), a sample of civilian and military youth first interviewed in early 1979 and reinterviewed annually; the NLSY Mothers and Children, a data set of information on the experiences of NLSY women as they become mothers and on the birth and early childhood experiences of their children; and the four Original Cohorts--NLS Older Men, NLS Young Men, NLS Mature Women, and NLS Young Women. Each section provides information on the samples, the interviews, and the major data elements available within each data set. Section 5 presents a bibliographic listing of recent research that used data from the NLSY, the NLSY Children, and the four Original Cohorts. Sections 6 and 7 describe the NLS CD-ROMs, magnetic tapes, and documentation items available to the public. Section 8 directs the reader to other publications, technical manuals, and reports providing more information on the NLS. (YLB)