Abstract. Subliminal perception is a long-standing topic in psychology, which has been strongly debated throughout the twentieth century. Recently, unconscious information processing has gained attention in human-computer interaction (HCI) research on the basis that subliminal stimulation can covertly trigger automatic responses without generating mental workload. The aim is to increase the interaction efficiency between humans and systems by embedding subliminal stimuli in user interfaces. Moreover, the currently thriving research on adaptive and symbiotic systems makes the interest for unconscious processes even greater.The purpose of the present paper is to give an overview of both the most recent findings about subliminal stimuli applied to concrete contexts and the main stimulation techniques to obtain unconscious perception. The techniques reviewed here are the binocular rivalry, visual masking, visual crowding, and rapid serial visual presentation with some latest variants of these classic paradigms.