The Harvard Service Food Frequency Questionnaire (HSFFQ) has been used in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) in North Dakota, Missouri, and Massachusetts. This project collaborated with those States to improve HSFFQ output to better facilitate nutrition education, food package decisions, and referrals; to design, implement, and evaluate the use of aggregate nutrition data for local and State practices and policy decisions; and to use prospective data to examine the relationships between diet and childhood obesity. The project developed a standardized version of the HSFFQ to make collecting and compiling aggregate data easier and to make data reports more useful. The project demonstrated that aggregating nutrition data at the State level is feasible. The calibration studies uncovered the need for further analyses to explain the performance of the tool in the diet assessment of low-income Hispanic and African-American children. Prospective analysis of the influence of diet on overweight in low-income preschool children, while inconclusive, demonstrated the ability to use aggregate nutrition data to explore important epidemiological hypotheses.