Almost nothing is known about the conditions under which a leader displays transformational or transactional behavior, let be why the leader behaves in that way. In response to this lacuna, the present project will reveal the mechanisms that drive transformational and transactional leadership behavior. Therefore, a major scientific shift is needed as such a study implies moving away from between-leader comparisons to a focus on the dynamic nature of transformational and transactional leadership behavior. Moreover, it will allow leadership trainings to change or train the mechanisms that underlie the behavior in order to ultimately change the behavior itself. In particular, the project will: (1) Identify working conditions and situations that impact transactional and transformational leadership behavior; (2) Study how these working conditions are interpreted or appraised by leaders and how these perceptions or appraisals relate to transactional and transformational leadership behavior; (3) Study factors that may impact the perceptions or appraisals of the leaders; (4) Study factors that may impact the link between perceptions or appraisals and leadership behavior.