When two masked, to-be-attended targets are presented within half a second of each other, report accuracy for the second target (T2) is impaired relative to when the two targets are presented farther apart in time or relative to when the first target (T1) can be ignored. This effect is known as the attentional blink (AB). An additional T2 accuracy deficit is observed if T1 and T2 are identical or highly similar on a task-relevant dimension. This effect is known as repetition blindness (RB). For both AB and RB, targets are typically imbedded in rapid serial visual presentation (RSVP) streams and the dual-task attention cost lasts approximately half a second. Given the high degree of superficial similarity, AB and RB are often considered to be related phenomena. Although research thus far has suggested that both phenomena reflect limits of the attentional system and how attention is allocated when needing to organize stimuli for entrance into awareness, these two phenomena are dissociable; RB is not simply an enhanced AB. Furthermore, investigations of AB and RB have taken quite different courses over the last two decades. The AB has been investigated extensively with a variety of experimental, behavioral, neurophysiological, and clinical approaches, and has become widely used as a paradigm of convenience with which to study other effects. In contrast, studies of RB have tended to manipulate the nature of the target information to understand the level of representation that supports RB. WIREs Cogni Sci 2011 2 336-344 DOI: 10.1002/wcs.129 For further resources related to this article, please visit the WIREs website.