The Health Utilities Index (HUI) is a multi-attribute health-status classification system and utility scoring system used to measure health-related quality of life (HRQL). It includes two versions: HUI2 and HUI3, which together describe nearly 1 million unique health states. HUI provides comprehensive, reliable, and valid measures of health status and HRQL, and is widely used in clinical studies and general population surveys. It is used to calculate quality-adjusted life years (QALYs) and is accepted for cost-utility and cost-effectiveness analyses. HUI is available in multiple languages and formats, including self-complete and interviewer-administered versions, with various recall periods. It is responsive to changes in health status and has been validated in numerous studies. HUI is a registered trademark of Health Utilities Inc. and is used in a wide range of health conditions and populations. The HUI system includes a health-status classification system, preference-based scoring functions, data collection questionnaires, and coding algorithms. HUI questionnaires are available in 16 versions, based on factors such as mode of administration, assessment viewpoint, and recall period. HUI is used in clinical studies, cost-effectiveness analyses, and general population health surveys. It is also used for individual patient assessments and has been adapted for use in various countries and languages. HUI is supported by Health Utilities Inc., which provides licensing, technical support, and research assistance. The HUI system is a comprehensive, validated, and widely used tool for measuring health status and HRQL.The Health Utilities Index (HUI) is a multi-attribute health-status classification system and utility scoring system used to measure health-related quality of life (HRQL). It includes two versions: HUI2 and HUI3, which together describe nearly 1 million unique health states. HUI provides comprehensive, reliable, and valid measures of health status and HRQL, and is widely used in clinical studies and general population surveys. It is used to calculate quality-adjusted life years (QALYs) and is accepted for cost-utility and cost-effectiveness analyses. HUI is available in multiple languages and formats, including self-complete and interviewer-administered versions, with various recall periods. It is responsive to changes in health status and has been validated in numerous studies. HUI is a registered trademark of Health Utilities Inc. and is used in a wide range of health conditions and populations. The HUI system includes a health-status classification system, preference-based scoring functions, data collection questionnaires, and coding algorithms. HUI questionnaires are available in 16 versions, based on factors such as mode of administration, assessment viewpoint, and recall period. HUI is used in clinical studies, cost-effectiveness analyses, and general population health surveys. It is also used for individual patient assessments and has been adapted for use in various countries and languages. HUI is supported by Health Utilities Inc., which provides licensing, technical support, and research assistance. The HUI system is a comprehensive, validated, and widely used tool for measuring health status and HRQL.