This paper summarizes recent psychological research and theory on the topic of consciousness and looks at three questions in second language learning related to the role of consciousness in input processing: whether conscious awareness at the level of 'noticing' is necessary for language learning (the subliminal learning issue); whether it is necessary to consciously 'pay attention' in order to learn (the incidental learning issue); and whether learner hypotheses based on input are the result of conscious insight and understanding or an unconscious process of abstraction (the implicit learning issue). I conclude that subliminal language learning is impossible, and that noticing is the necessary and sufficient condition for converting input to intake. Incidental learning, on the other hand, is clearly both possible and effective when the demands of a task focus attention on what is to be learned. Even so, paying attention is probably facilitative, and may be necessary if adult learners are to acquire redundant grammatical features. The implicit learning issue is the most difficult to resolve. There is evidence for it, as well as for a facilitative effect for conscious understanding, but accounting for implicit learning may entail abandonment of the notion of unconscious 'rules'of the type usually assumed in applied linguistics.