The purpose of the present research was to develop and validate a measure of teachers' motivation toward specific work tasks: The Work Tasks Motivation Scale for Teachers (WTMST). The WTMST is designed to assess the constructs of intrinsic motivation, identified, introjected, and external regulations, and amotivation toward six work tasks (i.e., class preparation, teaching, evaluation, class management, administrative, and complementary tasks). Three studies conducted among 657 teachers were used to develop and validate the WTMST. Overall, results reveal that the WTMST is composed of five reliable factors (internally consistent and temporally stable) for each of the six work tasks. The construct validity of the WTMST is also supported by simplex-like patterns of relations and correlations with theoretically related variables. In addition, the pattern of correlations among the WTMST subscales across the work tasks indicated that teachers' types of motivation are specific to work tasks. Implications for research on teachers' motivation are discussed.