Background and Rationale: Asthma is a substantial public health problem with adolescents having substantial asthma-related morbidity. Adolescence is a critical phase of transition to adulthood, marked by the development of cognitive and autonomous skills required to assume greater responsibility for asthma care. Asthma self-management, which plays a pivotal role in achieving asthma control, is suboptimal among adolescents. Investigating asthma self-management behavior during this period is particularly crucial, to help them manage their asthma. Despite this, there is a dearth of validated measures assessing asthma self- management skills tailored specifically for adolescents. Objective: This study aims to fill this gap by developing and a reliable and valid asthma self-management questionnaire specifically designed for adolescents with asthma aged 12-21. Method: The asthma self-management behavior framework will underpin the development of a novel adolescent self-management questionnaire. We will follow the seven-step approach outlined in published guidelines to compose and validate questionnaire items. To compose questionnaire items, we will draw on our team’s prior clinical and research experiences with adolescents, asthma, self-management, and questionnaire development, including our qualitative study and recently published systematic review. We will integrate TWU student researchers into all phases of our study throughout the three-year grant period. We will employ a participatory research approach through active involvement of adolescents with asthma in item writing. The items face and content validity will be established by having experts (n= 8) assess the clarity and relevance of questionnaire items with respect to the construct of interest. Cognitive interviews will be conducted with adolescents with asthma (n=10) to ensure the respondents interpret items in the manner that researchers intended. We will establish the questionnaire’s psychometric properties by evaluating the questionnaire's factorial validity using a sample of 300 adolescents (12-21 years old) living with asthma (n=150 each in exploratory and confirmatory factor analysis) recruited from schools, clinics, and national asthma organizations using purposive and snowballing techniques. Construct validity will be established by examining its relationships with relevant variables, such as quality of life and self-efficacy, while questionnaire reliability will be assessed through internal consistency and test-retest reliability tests. Significance: Adolescents are at a vulnerable yet opportune stage to learn asthma self-management. The newly developed and validated questionnaire will have the potential to facilitate assessment and feedback in multidisciplinary clinical settings and offer a research tool to more accurately understand adolescent asthma self-management.