In this study, we present the development and validation of an instrument for measuring teachers' interpersonal self-efficacy: the Questionnaire on Teacher Interaction-Self-Efficacy (QTI-SE). We used the Questionnaire on Teacher Interaction as a basis to construct items. Current scales on teacher self-efficacy in classroom management cover interpersonal self-efficacy mostly indirect or they specifically focus on the efficacy to convey relatively high levels of teacher agency (e.g., the teacher's ability to maintain or restore classroom discipline). The QTI-SE is an instrument measuring teachers' interpersonal self-efficacy more comprehensively and in a reliable and valid way.