Following a tradition established by Broadbent of understanding the fate of the unattended message, the effects of extraneous sound (especially speech) on cognitive processing are reviewed. Speech disturbs the encoding or registration of visual material, particularly in settings in which the sound and vision combine to have the property of a single object. The effect of irrelevant speech on short-term memory is confined to verbal or spatial tasks that require memory for serial order, and is most pronounced with sounds that exhibit change. This effect is not confined to speech, however, and a range of non-speech sounds can disrupt serial recall. Studies using complex tasks, though less common, are consistent in showing appreciable interference from irrelevant speech. The effect on reading is qualitatively dissimilar to that found with short-term memory. Implications for theory and practice are spelled out.