Implicit learning is said to occur when a person learns about a complex stimulus without necessarily intending to do so, and in such a way that the resulting knowledge is difficult to express. Over the last 30 years, a number of studies have claimed to show evidence of implicit learning. In more recent years, however, considerable debate has arisen over the extent to which cognitive tasks can in fact be learned implicitly. Much of the debate has centred on the questions of how unconscious, and how abstract, is implicitly acquired knowledge? The aim of this book is to provide students and researchers with a self-contained and balanced summary of the various theoretical and empirical positions that are currently shaping this exciting area of research.