The National Education Longitudinal Studies (NELS) program is a long-term effort that now encompasses the educational experience of youth from three decades, the 1970s, 1980s, and 1990s. The NELS program studies the educational, vocational, and personal development of students at various grade levels, and the personal, familial, social, institutional, and cultural factors that may affect that development. The NELS program currently consists of three major studies: (1) the National Longitudinal Study of the High School Class of 1972 (NLS-72); (2) High School and Beyond (HS&B); and (3) the National Education Longitudinal Study of 1988 (NELS:88). This monograph discusses opportunities for drawing comparisons across the cohorts that comprise the three studies, as well as some of the differences in survey content and design that may limit the possibilities of drawing valid comparisons. At the student level, cohorts can be compared on an intergenerational or cross-cohort time-lag basis. Fixed-time comparisons are also possible, and longitudinal comparative analysis of the cohorts can be performed by modeling the history of the age/grade cohorts. Comparisons among institutions are also possible, and possible time points for comparison are identified. The overall sample designs are essentially similar for the three studies, but some differences in school and subgroup sampling are identified, especially as they pertain to high school seniors. Cautions in comparisons due to differing response rates and student characteristics are outlined. The first appendix discusses item overlap among the NELS:88 second followup and HS&B and NLS-72. The second appendix discusses NELS:88 first followup item overlap with HS&B base year sophomore items. (Contains 6 tables, 1 figure, and 32 references.) (SLD)