Sleep is vital for all aspects of human health, but it is often suggested that it has the most profound effect on our mood. Poor sleep quality, such as having difficulties initiating or staying asleep or having non-restorative sleep, is associated with a reduction in positive affect and an increase in negative affect during the day. How sleep impacts our emotional functioning during the day is however still an open question. A growing literature demonstrates that the ability to regulate one’s emotions might be an important mechanism in the relationship between poor sleep and mood disturbance. Emotion regulation refers to the actions and thoughts we perform to influence what emotions we have, when we have them, and how we express them. Emotion regulation is often suggested to be a central aspect of employees in social jobs, so people who work with clients, customers, patients, students etc. Employees use emotion regulation strategies in order to behave appropriately at work and perform their work role (e.g., staying friendly towards demanding customers). In this PhD project, mixed methods (cross-sectional, experience sampling, experimental) and objective sleep measures (polysomnography, actigraphy) will be used to assess (1) whether there is a bidirectional relationship between sleep and emotion regulation, (2) what sleep factors (i.e., sleep quality, sleep quantity, sleep regularity) have the strongest impact on adaptive emotion regulation and (3) and whether an emotion regulation training improves the sleep quality of employees.