The Experience Sampling Method (ESM) allows the examination of ongoing thoughts, feelings and actions as they occur in the course of everyday life. A prime benefit is that it captures events in their natural context, thereby complementing information obtained by more traditional techniques. We used ESM to study time and mood at work. Our data were collected by sending 30 text messages over 10 working days to each of 168 part-time workers. On each occasion, respondents assessed their mood. We explored the joint effects of three sets of variables: activities in which people are engaged; individual differences; and time (i.e., when mood is measured). Since the data in our study can be thought of as being collected at two levels, we applied techniques of hierarchical linear models. The results indicated that activities were significant but no systematic individual differences were detected. There were some small diurnal effects as well as an overall â€œFriday effect.â€� Lastly, the weather had little or no influence on self-reported mood state. We discuss the results in terms of their methodological implications for studying daily life.