The establishment of WEB2.0 and the launch of various online 3D platforms in the last few years show that virtual environments are getting increasingly popular these days. Businesses as well as research institutions have recognized this trend and a variety of projects have already been started in this field. However, in order to be able to participate successfully in virtual worlds, an understanding of the basic concepts, especially interaction, is crucial. Hence, this book provides the reader with a description of virtual interaction techniques and a variety of related concepts, such as avatars and computer animation. Explanations of theory are supplemented with an analysis of the concepts in Second Life, one of the currently largest virtual 3D worlds. Finally, the book presents a detailed description of a virtual theater performance, where the opportunities and restrictions of virtual worlds are explored and the reader gets an impression how the described interaction techniques can effectively be implemented and used.