This report includes: (1) a description of the way overweight and obesity have been measured by various investigators, including an assessment of the reliability and validity of the available measures; (2) data on the prevalence of overweight based on a literature review, including a list of issues that may influence estimates of prevalence (e.g., type of measure used, age of population); (3) a summary of the relationships among overweight, obesity, and health, including a review of the relationship between weight reduction and future health status; (4) a description of the Rand Health Insurance Study (HIS) measures of weight and overweight, including summary statistics for the measures based on data collected at the time of enrollment into the HIS of people aged 14 to 61; (5) tests of the reliability and validity of the HIS measures; (6) a brief description of the experimental hypotheses to be tested; and (7) a discussion of the measurement of eating habits. (Author)