The most recent survey effort to determine the extent of food insecurity and hunger in the United States, the Food Security Supplement, included a series of questions to assess this complex phenomenon. The primary measure developed from this Food Security Supplement was based on measurement concepts, methods and items from two previously developed measures. This paper presents the evidence available that questionnaire-based measures, in particular the national food security measure, provide valid measurement of food insecurity and hunger for population and individual uses. The paper discusses basic ideas about measurement and criteria for establishing validity of measures and then uses these criteria to structure an examination of the research results available to establish the validity of food security measures. The results show that the construction of the national food security measure is well grounded in our understanding of food insecurity and hunger, its performance is consistent with that understanding, it is precise within usual performance standards, dependable, accurate at both group and individual levels within reasonable performance standards, and its accuracy is attributable to the well-grounded understanding. These results provide strong evidence that the Food Security Supplement provides valid measurement of food insecurity and hunger for population and individual uses. Further validation research is required for subgroups of the population, not yet studied for validation purposes, to establish validity for monitoring population changes in prevalence and to develop and validate robust and contextually sensitive measures in a variety of countries that reflect how people experience and think about food insecurity and hunger.