Virtual reality technology has been developed commercially since the early 1990s but it is only recently, with the popularity of the internet, that it has become feasible to link many users simultaneously in shared virtual environments. This raises a number of interesting questions such as: what is the difference between face-to-face and avatar-to-avatar interaction? What patterns govern the formation of virtual communities? How does the appearance of the avatar change the nature of the communication? There has been much speculation about issues such as these but research is still at a relatively early stage. This is the first book to bring together work from relevant disciplines to form a reference guide for practitioners, students and researchers interested in how we interact in computer-generated environments. It contains contributions from most of the key people in this area (including Microsoft Research's Virtual Worlds Group) and presents their findings in a way which is accessible to readers who are new to this field or who come from related areas. It is divided into 2 parts; chapters 2-6 deal with internet-based virtual worlds which have been widely used by the public; chapters 7-10 deal with networked VR systems which have been primarily used in pilot studies and research. Some chapters take the viewpoint of a participant observer, whilst others take a more experimental approach and assess the results of relevant trials. This book will be essential reading for anyone involved in developing, using or researching virtual worlds, and will also be of interest to students on courses such as VR and Computer-mediated communication.