Abstract This paper describes a system we have implemented that enables people to share structured in-place annotations attached to material in arbitrary documents on the WWW. The basic conceptual decisions are laid out, and a prototypical example of the client-server interaction is given. We then explain the usage perspective, describe our experience with using the system, and discuss other experimental usages of our prototype implementation, such as collaborative filtering, seals of approval, and value-added trails. We show how this is a specific instantiation of a more general “virtual document” architecture in which, with the help of light-weight distributed meta information, viewed documents can incorporate material that is dynamically integrated from multiple distributed sources. Development of that architecture is part of a larger project on Digital Libraries that we are engaged in.