Although it has been known for 100 years that cognitive functioning is impaired in schizophrenia, the implications of this impairment have only recently been clearly understood. While in the past, cognitive deficits were thought to be the result of other aspects of the illness, such as poor co- operation, or as a result of the treatment of the illness, it is now known that these factors exert only a very minor influence on cognitive deficit. This book, with contributions from the major international names in the field, reviews the most recent research on the impairment of cognitive functioning in schizophrenia, covering: what it is, how wide-ranging it can be, what the clinical implications are, and how it can be treated? The book is divided into three sections. The first section provides background information on the important aspects of cognitive functioning in schizophrenia. The second section provides information on the correlates of cognitive functioning, examining classical symptoms of the illness, as well as social and adaptive functional deficits. The final section provides information on the treatment of cognitive functioning in schizophrenia, from the older less effective treatments with conventional antipsychotics, to the developing treatment strategies using experimental compounds. A clear insight into cognitive deficit is the key to understanding why previous treatments have failed, and the key by which new treatments may change this terrible illness, treatments significantly more effective than earlier interventions.