The ways that extraneous visual and auditory stimuli impair human performance are reviewed with aim of distinguishing those sensory, perceptual and cognitive effects relevant to the design of human-machine systems. Although commonly regarded as disruptive, distractions reflect the adaptability of the organism to changing circumstances. Depending on the context, our knowledge of the ways in which distraction works can be exploited in the form of alarms or other attention-getting devices, or resisted by changing the physical and psychological properties of the stimuli. The research described here draws from contemporary research on distraction. The review underscores the vulnerability of performance even from stimuli of modest magnitude while acknowledging that distraction is a necessary consequence of our adaptive brain that leads to effects that are (and sometimes, but not always) beneficial to safety, efficiency and wellbeing. Low intensity distractors are particularly sensitive to the context in which they occur. The mechanisms outlined can be exploited either to grab attention (and even temporarily disable the individual, but more usefully to warn or redirect the individual) or to modify it in subtle ways across the gamut of human activity.