This book is about multimedia communication using the Internet. We wrote this book for (at least) three reasons. Firstly, we use the Internet to communicate and have done so for many years. Increasingly, we find ourselves using it as a replacement for the telephone, for conferencing and for delivering classes and seminars to remote participants. We think that this is the way that communication will be achieved in general for a wide variety of applications in the future, and feel that this view is worth reading about. Secondly, we work in education and teach students about the principles behind communication and multimedia, and wanted to share the ideas and explanations with a broader readership than just the students who read our notes. Finally, we are all involved in researching and developing Internet protocols and mechanisms to improve multimedia communication applications and services, and wanted to explain the state of the art and trends to a wider audience.