Purpose: Teachers' organisational identification is crucial for the success of educational reform in the change process. This study investigates how and under what conditions authentic principal leadership contributes to teachers' organisational identification. Design/methodology/approach: Data collected from 7907 public high school teachers across Türkiye were analysed using bootstrapping method. This research tested a moderated mediation model of authentic principal leadership effects on teachers' organisational identification by incorporating teacher academic optimism as a mediator, and teacher collective responsibility as a moderator. Findings: Results revealed significant direct and indirect effects of authentic principal leadership on the teachers' organisational identification via teacher academic optimism. Teacher collective responsibility significantly moderated the effects of authentic principal leadership on both teacher academic optimism and on teachers' organisational identification. The positive effects of authentic principal leadership were strengthened when the collective responsibility was higher. Originality/value: This study integrates authentic leadership theory with social identity theory, which provides a more theoretically accurate understanding of how authentic principal leadership influences teachers' organisational identification.