Doctor of Philosophy / Department of Psychological Sciences / Clive J. A. Fullagar / In the constantly changing world of work, employees are expected to be proactive by taking initiative and being self-starting, future focused, and change oriented. Consequently, research around proactivity has grown exponentially over the last two decades. However, the relationship with employee well-being has been widely neglected. This research addressed this gap by investigating the dynamics between employee proactivity and subjective well-being, while taking work-related flow into account. With the use of a diary method, this study provided support that proactivity is not necessarily a burden on psychological well-being. Instead, proactivity in its dispositional and behavioral form of task crafting, was found to have a direct impact on optimal work experiences and well-being outcomes such as subjective vitality and positive affect. Acknowledging the complexity of the relationships, this study also tested mediated and moderated paths and provided several theoretical and practical contributions.