This manual has been produced to familiarize data users with the procedures followed for data collection and processing for the base year through second follow-up of the Education Longitudinal Study of 2002 (ELS:2002). It also provides the necessary documentation for use of the data files, as they appear on the ELS:2002 base-year to second follow-up electronic codebook (ECB) (NCES 2008-346), and information that may be helpful to users of the ELS:2002 Data Analysis System (DAS). Chapter 1 serves as an introduction to the Education Longitudinal Study of 2002 (ELS:2002). It includes an overview and history of the National Center for Education Statistics program of longitudinal high school cohorts, summarizes the ELS:2002 objectives, and supplies an overview of the base-year and longitudinal study design. Chapter 2 describes the data collection instruments, including both the development and content of the tests and questionnaires used in the three rounds of data collection. It also documents the first follow-up transcript and course offerings studies and provides information about linkages to external data sources. The sample design is documented in chapter 3, while data collection procedures and results are presented in chapter 4. Chapter 5 describes data preparation and processing, including data file preparation. Chapter 6 provides an account of the weighting procedures used in the study, with special emphasis on the most recent (2006) round. The chapter also covers statistical procedures, such as imputation, disclosure avoidance, and the calculation of design effects. Chapter 7 describes the contents of the data files, including the data structure and analysis populations. The appendixes include, among other topics, an introduction to the base-year to second follow-up electronic codebook (ECB); a flow chart and facsimile for the second follow-up instrument; a crosswalk between occupation coding schemes; a glossary of terms; information about making cross-cohort comparisons; a listing of the superset of variables to be found on the ELS:2002 second follow-up restricted-use ECB and the subset of the same variables provided by the ELS:2002 second follow-up Data Analysis System (DAS); a description of the second follow-up composite variables; and a synopsis of the ELS:2002 second follow-up field test. Appended are: (1) Cross-Cohort Comparisons; (2) Quick Guide to Using the ELS:2002/06 Data; (3) Synopsis of the ELS:2002 Second Follow-up Field Test Report; (4) Data File Documentation Errata; (5) Flow Chart and Facsimile for the Second Follow-up Questionnaire; (6) Occupational Coding Crosswalk; (7) Transcript Standard Errors and Design Effects; (8) Propensity Models Versus Weighting Cell Approaches to Nonresponse Adjustment: A Methodological Comparison; (9) Average Weight Adjustment Factors; (10) Standard Errors and Design Effects; (11) Nonresponse Bias Tables; (12) Variable List for the ELS:2002 Electronic Codebook (ECB) and Data Analysis System (DAS); (13) Second Follow-up Composite Variables; (14) Data Imported Into ELS:2002 From External Sources; and (15) Glossary of Terms. [To access "Education Longitudinal Study of 2002: Base-Year to First Follow-Up Data File Documentation. NCES 2006-344," see ED489083.]