This volume in the NATO Special Programme on Advanced Educational Technology addresses fundamental principles in the design of a dialogue component in intelligent tutoring systems. The purpose of the book is to link fundamental issues of communication and interaction to the more restricted domain of instructional dialogue. The papers are grouped into parts on: theoretical issues in instructional dialogue; theory into practice - interaction in learning environments; natural dialogue and interaction theory; and feedback and control in human-machine communication. The book originates from a NATO Advanced Research Workshop held in Italy in 1992 and the authors are leading researchers in educational technology, dialogue research and user-interface design.