When and why does the experience of helping others at work spill over into positive affect at home? This paper presents a within-person exam- ination of the association between perceived prosocial impact at work and positive affect at home, as well as the psychological mechanisms that mediate this relationship. Sixty-eight firefighters and rescue workers completed electronic diaries twice a day over the course of 1 working week. Random-coefficient modeling showed that perceived prosocial impact predicted positive affect at bedtime. This relationship was medi- ated by perceived competence at the end of the working day and positive work reflection during after-work hours but not by positive affect at the end of the working day. The findings d...