This practical manual is designed as a guide for those working with one or more of the National Longitudinal Surveys (NLS) data sets. Section 1 is a discussion of the sample design, sampling methodology, and field procedures used during the surveys of each NLS cohort. Weighting, sample representativeness, and attrition are discussed, and a series of tables depict the number or respondents who continued to be interviewed at each interview point as well as the number of those not interviewed and why they dropped out of the study. Section 2 is a topical guide to the NLS that presents, for each cohort, a description of the primary variables available on select topics. Section 3 has four purposes: (1) discusses the several types of created variables present within the various NLS data sets; (2) depicts, by survey year, the primary created variables present within the NLS main data files and the four Original Cohort data sets; (3) provides a crosswalk to the places within the documentation system where a user can find derivations for many main file variables; and (4) presents additional creation procedures for some important main file variables. Section 4 provides information on how to access NLS variables via the extensive hardcopy and electronic documentation system. Section 5 provides information on the format and structure of the various NLS magnetic tapes. Appendixes include NLSY file descriptions 1979-1991 and NLSY and Original Cohort dictionaries of acceptable keywords. (YLB)