The concept of «virtuality» has introduced a completely new mode of representing, presenting, as well as acquiring knowledge. The present collection of papers acknowledges this development and gives a survey over the most important developments, issues, and foundations from an interdisciplinary perspective. This book intends to enlarge the definition of virtual reality in order to go beyond the toy character it may still have in the public. The contributions show that virtuality has not only been successfully applied in various technical and medical domains but also touches basic philosophical problems and questions related to cognitive science. In fact, developing the concept of virtuality further will be the key to many challenges in both theoretical and technical domains.