this book focuses on the use of technology-mediated interaction in distance education and open learning. special emphasis is placed on models for collaborative dialogues in general and learning dialogues in particular, at a distance, through a computer network. the technology is thus used as a medium for conducting conversations and dialogues, allowing the co-construction of new knowledge and understanding among groups of learners and tutors, who might otherwise have little opportunity to interact with each other. the book has three main aspects: it gives an overview of the state of the art; it integrates the viewpoints of educationalists, users, and scientists; and it offers a balance between fundamental research and applications. it is part of the nato special programme on advanced educational technology.