A food frequency questionnaire (FFQ) is a dietary assessment tool that asks respondents how often they consume items from a defined list of foods over a reference period, typically the past month or year. Responses — ranging from “never” to “several times a day” — are converted into estimates of nutrient and food-group intakes using standard portion sizes and composition data. FFQs are cheap to administer to large populations and capture habitual diet better than a single day’s recall, which makes them the workhorse of nutritional epidemiology. Their weaknesses are reliance on memory, difficulty estimating portions, and limited food lists that may miss ethnic or novel foods. Researchers validate FFQs against weighed records or biomarkers before trusting their results.