The classic theory of spatial attention hypothesized 2 modes, voluntary and involuntary. Folk, Remington, and Johnston (1992) reported that even involuntary attention capture by stimuli requires a match between stimulus properties and what the observer is looking for. This surprising conclusion has been confirmed by many subsequent studies. In these studies, however, the observer typically looks for the same property throughout an entire session. Real-world behavior, in contrast, often requires frequent shifts in attentional set. The present study examined whether such shifts weaken attentional settings, allowing task-irrelevant objects to capture attention. Surprisingly, fluctuating control settings did not increase vulnerability to capture by salient stimuli (color singletons and abrupt onsets). We conclude that the attention control system is remarkably flexible, able to rapidly and fully adopt new settings and abandon old settings. (Contains 4 tables and 5 figures.)