The Health Literacy Questionnaire (HLQ) is a comprehensive measure of health literacy designed to diagnose health literacy needs across individuals and organizations. The development of the HLQ involved a validity-driven approach, including grounded consultations, workshops, and interviews with the general population, patients, healthcare practitioners, and policymakers. The initial 91 items were reduced to 44 items through psychometric analyses, including confirmatory factor analysis (CFA) and item response theory. The final HLQ consists of 9 scales covering areas such as feeling understood and supported by healthcare providers, having sufficient information to manage health, actively managing health, social support for health, appraisal of health information, ability to engage with healthcare providers, navigating the healthcare system, finding good health information, and understanding health information well enough to know what to do. The HLQ was tested in a calibration sample (N=634) and a replication sample (N=405), showing good psychometric properties. The HLQ is expected to be useful in surveys, intervention evaluations, and studies of health literacy needs and capabilities.The Health Literacy Questionnaire (HLQ) is a comprehensive measure of health literacy designed to diagnose health literacy needs across individuals and organizations. The development of the HLQ involved a validity-driven approach, including grounded consultations, workshops, and interviews with the general population, patients, healthcare practitioners, and policymakers. The initial 91 items were reduced to 44 items through psychometric analyses, including confirmatory factor analysis (CFA) and item response theory. The final HLQ consists of 9 scales covering areas such as feeling understood and supported by healthcare providers, having sufficient information to manage health, actively managing health, social support for health, appraisal of health information, ability to engage with healthcare providers, navigating the healthcare system, finding good health information, and understanding health information well enough to know what to do. The HLQ was tested in a calibration sample (N=634) and a replication sample (N=405), showing good psychometric properties. The HLQ is expected to be useful in surveys, intervention evaluations, and studies of health literacy needs and capabilities.