Attention may be distracted from its intended focus both by stimuli in the external environment and by internally generated task-unrelated thoughts during mind wandering. However, previous attention research has focused almost exclusively on distraction by external stimuli, and the extent to which mind wandering relates to external distraction is as yet unclear. In the present study, the authors examined the relationship between individual differences in mind wandering and in the magnitude of distraction by either response-competing distractors or salient response-unrelated and task-irrelevant distractors. Self-reported susceptibility to mind wandering was found to positively correlate with task-irrelevant distraction but not with response-competition interference. These results reveal mind wandering as a manifestation of susceptibility to task-irrelevant distraction and establish a laboratory measure of general susceptibility to irrelevant distraction, including both internal and external sources.