The 5-item World Health Organization Well-Being Index (WHO-5) is a widely used questionnaire for assessing subjective psychological well-being. This systematic review evaluates the clinimetric validity, responsiveness, sensitivity, and applicability of the WHO-5 across various study fields. The review found that the WHO-5 has high clinimetric validity, can effectively balance the effects of treatments, is a sensitive and specific screening tool for depression, and is applicable in a wide range of research studies. The WHO-5 consists of five simple, non-invasive questions that measure positive well-being and has been translated into over 30 languages. It has been used in clinical trials, depression screening, and various other fields, demonstrating its broad utility and reliability.The 5-item World Health Organization Well-Being Index (WHO-5) is a widely used questionnaire for assessing subjective psychological well-being. This systematic review evaluates the clinimetric validity, responsiveness, sensitivity, and applicability of the WHO-5 across various study fields. The review found that the WHO-5 has high clinimetric validity, can effectively balance the effects of treatments, is a sensitive and specific screening tool for depression, and is applicable in a wide range of research studies. The WHO-5 consists of five simple, non-invasive questions that measure positive well-being and has been translated into over 30 languages. It has been used in clinical trials, depression screening, and various other fields, demonstrating its broad utility and reliability.