Research on collaborative learning is currently a very popular topic in education, psychology and computer science. In recent years, educational research has attempted to determine under what circumstances collaborative learning is more effective than learning alone, and more recently, numerous studies have focused on computer-mediated collaborative learning. In psychology, interest in collaborative learning is related to the emergence of new theories such as 'shared cognition' and 'distributed cognition'. These theories move away from the view traditionally held in cognitive science according to which human cognition is bound inside individual heads. The word 'collaboration' is also used very frequently in computer science to describe the interactions among artificial agents. The term has often been used rather loosely in the different research communities: this book is a contribution towards refining and operationalizing the concept.