This occasional paper updates and extends earlier papers in the Monitoring the Future project. It provides a detailed description of the project's design, including sampling design; data collection procedures; measurement content; and questionnaire format. It attempts to include sufficient information for others who wish to evaluate the results, to replicate aspects of the study, or to analyze data that is archived. Although there have been additions to the study design and procedures, the basic study design described in a 1978 paper has remained constant in its fundamental characteristics, which is considered the key condition for its ability to successfully measure change. Following an introduction and overview, this paper presents the scope, purposes, and rationale for the nationwide sampling of 8th, 10th, and 12th grade students. In the measures section, an overview is presented of the conceptual framework of the study, the outline of questionnaire content, the questionnaire organization, and the consent and format of the 8th and 10th grade questionnaires. Sampling and data collection procedures are included in the next section, which is followed by the representativeness and validity. (Contains 2 tables, 3 figures, and 106 references.) (JDM)