It is widely acknowledged that educational quality depends on the quality of teachers. Their wellbeing is one of the most crucial ways for achieving such quality. However, both early-career teachers as well as experienced teachers face different professional identity tensions throughout their career, which is assumed detrimental for their wellbeing and can cause burnout. Undesirable dropouts of early-career teachers and burnout of experienced teachers, in both primary education, secondary education and vocational education, cause teacher shortages. This study investigates how wellbeing and burnout of early career teachers and experienced teachers in primary, secondary and secondary vocational education are related to their professional identity tensions. It further reveals effects of two six-week intervention programmes, including a ‘passion for teaching week’ (experienced teachers) and a gratitude week (early-career teachers), based on gratitude theory and positive-activity theory, on teacher wellbeing and burnout. A mixed-method design, including longitudinal studies, quasi-experimental studies and qualitative studies is used, in which insights stemming from educational sciences, positive psychology and organisational psychology are combined. This fundamental and multidisciplinary interlinked research project aims to increase our understanding of teacher burnout, wellbeing and the underlying professional identity tensions, by comparing early-career teachers and experienced teachers in three educational domains, which is assumed to contribute to a stronger teacher workforce and, as such, to improve educational quality.