The Early Childhood Longitudinal Study (ECLS-K), Kindergarten Class of 1998-99, selected a nationally representative sample of approximately 22,000 kindergartners in the fall of 1998 and is following these children through the end of the fifth grade. Baseline data about these children, their families, and their kindergarten programs were collected by means of telephone interviews with the children's parents/guardians and from self-administered questionnaires completed by the kindergarten teachers. Data were also gathered during an individual assessment with each child. This CD-ROM contains the complete ECLS-K base year public-use electronic code book (ECB), and includes the data files, the electronic code book, and files with complete documentation. The ECLS-K base year public-use documentation is in portable document format (PDF). The ECB documentation is in chapter 8 of the use guide contained on the userguide.pdf file on the CD-ROM. Documentation included with the CD-ROM provides instructions for installation and a selected directory listing of the content of the CD-ROM. (KB)