Internet computing is at the core of information revolution which changes the way we communicate, work, learn, do business, and play. A major trend in Internet computing is to use the Internet to enhance human-to-human interaction, communication, and collaboration. Collaborative computing represents a shift in emphasis from using computers to support individual users’ work to using computers to support group users’ interaction and collaboration. The integration of Internet computing and collaborative computing has led to the emerging and rapidly expanding area of collaborative Internet computing, which studies computing technologies and applications for supporting geographically dispersed people to work and play together over the Internet. Professor Sun's research team has been working in this area since 1994, under the umbrella of the REDUCE (REal-time Distributed Unconstrained Collaborative Environment) project, which aims to investigate the underlying principles and techniques for supporting human-to-human interaction and collaboration over the Internet, and to design and implement collaborative Internet computing systems for evaluating and demonstrating the research results. His paper explores a range of fundamental and challenging issues in collaborative Internet computing applications.