How often are creative ideas generated during episodes of mind wandering, and do they differ from those generated while on task? In two studies ( N = 98, N = 87), professional writers and physicists reported on their most creative idea of the day, what they were thinking about and doing when it occurred, whether the idea felt like an "aha" moment, and the quality of the idea. Participants reported that one fifth of their most significant ideas of the day were formed during spontaneous task-independent mind wandering-operationalized here as (a) engaging in an activity other than working and (b) thinking about something unrelated to the generated idea. There were no differences between ratings of the creativity or importance of ideas that occurred during mind wandering and those that occurred on task. However, ideas that occurred during mind wandering were more likely to be associated with overcoming an impasse on a problem and to be experienced as "aha" moments, compared with ideas generated while on task.