In this paper, we tested Kahn's (1990) proposition that levels of personal role engagement are influenced by fluctuating perceptions of meaningfulness, safety and availability through the working day. We hypothesized that meaningfulness, safety and availability perceptions would be directly associated with engagement and also that they would mediate the associations between specific job factors, notably job design and fit, social support, and personal and organizational resources, and engagement. A total of 124 participants each completed a quantitative work diary relating to the most and least engaging situations every day within six working days (n = 723 occasions). Multilevel analysis of the findings showed that meaningfulness and availability, but not safety, may be important for boosts and drops in levels of engagement, and that job design, job fit and personal resources play an especially critical role. Organizational resources, co-worker support, and safety were not associated with fluctuations in the level of engagement.