OBJECTIVES AND OVERVIEW Because of its growth in size, scope, and complexity--as well as its increasingly central role in society--the Internet has become an important object of study and evaluation. Many significant innovations in the networking community in recent years have been directed at obtaining a more accurate understanding of the fundamental behavior of the complex system that is the Internet. These innovations have come in the form of better models of components of the system, better tools which enable us to measure the performance of the system more accurately, and new techniques coupled with performance evaluation which have delivered better system utilization. The continued development and improvement of our understanding of the properties of the Internet is essential to guide designers of hardware, protocols, and applications for the next decade of Internet growth. As a research community, an important next step involves an comprehensive look at the challenges that lie ahead in this area. This includes an an evaluation of both the current unsolved challenges and the upcoming challenges the Internet will present us with in the near future, and a discussion of the promising new techniques that innovators in the field are currently developing. To this end, the Web and InterNetworking Research Group at Boston University (WING@BU), with support from the National Science Foundation, (grant #9985484) organized a one-day workshop which was held at Boston University on Monday, August 30, 1999 (immediately preceding ACM SIGCOMM '99).