This PhD will focus on the effect that transformational leadership has on employee well-being. Transformational leadership entails improving employee performance beyond expectations through vision and mission and through challenging followers to think outside of the box. The link between transformational leadership and employee performance has received broad empirical support over the last decades. It is however unclear whether performance ‘beyond expectations’ is only possible at the expense of employee well-being. It is furthermore unclear whether the link between transformational leadership and employee well-being depends on various conditions (e.g., employee characteristics or organisational context) and whether it varies over time. Hence, this PhD will explore the transformational leadership well-being link in much depth (e.g., application of a diary study/longitudinal research design) and consider modifications to the transformational leadership construct to incorporate the promotion of employee well-being. This research is particularly relevant in light of the high organisational costs resulting from poor well-being and the popularity of transformational leadership training.