Purpose: The aim of this study was to develop and validate a scale to assess work role motivation in school principals: the Work Role Motivation Scale for School Principals (WRMS-SP). The WRMS-SP is designed to measure intrinsic motivation, three types of extrinsic motivation (identified, introjected, and external), and amotivation with respect to three work roles (administrative, instructional leadership, and informative). Research Design: Data were gathered via a sample of 570 French Canadian school principals who completed an online questionnaire. Findings: Confirmatory factor analyses support (a) the 15-factor scale structure (5 types of motivation x 3 roles), (b) factor structure invariance over gender and job position, and (3) construct validity through a multitrait-multimethod matrix method analysis, which confirms the convergent and discriminant validity of the constructs and supports simplex patterns with respect to the roles, as well as intercorrelations between subscales and external criteria. Conclusions: The WRMS-SP is a promising instrument that could deepen our understanding, both theoretical and applied, of the professional functioning of principals and the repercussions on school success and improvement. (Contains 4 tables.)