A series of studies is reviewed strongly suggesting that event-related potentials (ERPs) may provide markers for unconscious processes. In one study it was shown that, although smaller in amplitude by a least a factor of four, ERPs to subliminal stimuli have a similar component structure to ERPs to supraliminal stimuli. In another study, it was shown that an oddball P300 could be obtained for subliminal stimuli. In two additional studies, it was shown that aversive conditioning could be established unconsciously. The implications for our understanding of the role of unconscious processes in phobias and post-traumatic stress disorders are discussed, as well as more general implications for memory formation.