The article describes the development and validation of the Warwick-Edinburgh Mental Well-being Scale (WEMWBS), a new scale designed to measure mental well-being. The scale consists of 14 positively worded items covering aspects of positive mental health, including positive affect, interpersonal relationships, and positive functioning. The scale was developed by an expert panel and validated through focus groups and psychometric testing. It was tested on a student sample and a representative population sample. The results showed good content validity, high internal consistency (Cronbach's alpha = 0.89 for students, 0.91 for the population), and high correlations with other mental health and well-being scales. The scale also demonstrated test-retest reliability (r = 0.83) and was less susceptible to social desirability bias compared to other scales. The WEMWBS is a promising tool for monitoring mental well-being at the population level, but further research is needed to establish its sensitivity to change.The article describes the development and validation of the Warwick-Edinburgh Mental Well-being Scale (WEMWBS), a new scale designed to measure mental well-being. The scale consists of 14 positively worded items covering aspects of positive mental health, including positive affect, interpersonal relationships, and positive functioning. The scale was developed by an expert panel and validated through focus groups and psychometric testing. It was tested on a student sample and a representative population sample. The results showed good content validity, high internal consistency (Cronbach's alpha = 0.89 for students, 0.91 for the population), and high correlations with other mental health and well-being scales. The scale also demonstrated test-retest reliability (r = 0.83) and was less susceptible to social desirability bias compared to other scales. The WEMWBS is a promising tool for monitoring mental well-being at the population level, but further research is needed to establish its sensitivity to change.