The National Longitudinal Surveys (NLS), sponsored by the Bureau of Labor Statistics, U.S. Department of Labor, are a set of surveys each of which has gathered information at multiple points in time on the labor market experiences of five groups of men and women since the mid-1960s. Each group of at least 5,000 persons was selected to be representative of all U.S. citizens born during a given time period such that conclusions drawn about the sample group would be generalizable to the experiences of the larger population. This user's guide is designed for researchers who are either working with one or more of the NLS data sets or exploring the applicability of the NLS to their research needs. The guide is organized in four sections, each beginning with a chapter-specific table of contents and list of tables. The first section provides a brief overview of the set of surveys of the NLS and the various data sets that are currently available to the public. This section also reviews the following three sections of the guide and provides a list of resource materials distributed through NLS User Services. Section 2 presents practical information on the various methods of accessing NLS variables; Section 3 describes (in 35 alphabetically arranged topical discussions) the types of information that have been collected for each cohort. Section 4 presents information necessary to extract NLS variables from magnetic tapes. Appendixes describe the variables found within each NLS record type, present alphabetically arranged lists of keywords for the NLSY (Youth) and Original Cohort main data files, and provide a brief glossary of NLSY terms. (KC)