This study describes the fascinating learning, memory and performance processes which take place without the subject's "explicit" awareness. A well-known example is patients under anaesthetic who, without being able to verbally recall the surgeons' conversation, do show some retention of the conversation. How much of what we "know" has been learned implicitly? How much of our problem-solving abilities are founded on unconscious processes? The contributors attempt to answer these and other questions, providing an informative overview of a controversial area.