A food frequency questionnaire is a dietary assessment tool commonly used in nutrition research that consists of a questionnaire in which participants are asked to answer questions relating to the frequency with which they consumed certain foods and drinks during a selected time period, e.g. a week, month or year. Food frequency questionnaires can be long or short and interviewer- or self-administered. They are commonly used to investigate the dietary patterns of large populations, and unlike 24-hour recalls, they can measure the consumption of foods that are eaten incidentally or occasionally. Limitations of food frequency questionnaires include their reliance on participants’ ability to accurately recall the foods and drinks they have consumed over a relatively long period, and the possibility of social desirability bias (e.g. people may over-report their consumption of foods they think are healthy or sustainable).