Implicit learning is said to occur when someone learns about a complex stimulus without the intention of doing so, and in such a way that the knowledge is difficult to express. A number of studies have claimed to show evidence of implicit learning, but more recently, considerable debate has arisen over the extent to which cognitive tasks are learned implicitly. Most of the debate centers on the questions of how unconscious, and how abstract, is implicit knowledge. This book provides 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.