Distributed file systems have come into widespread use in recent years. Many allow files to be accessed over large geographic areas and across organizational boundaries. However, few systems to date have given much thought to how information should be organized in such a global environment. This paper describes the Prospero File System, a file system based on the Virtual System Model, a model for building large systems within which users construct their own virtual systems by selecting and organizing the objects and services of interest. This customized view of a globaJ file system makes it easier for users to keep track of files that they have identified as being of interest. The use of multiple name spaces can cause confusion. Such confusion is eliminated by support for closure: ever) ' object has an associated name space, and names specified by the object are resolved in that name space. Tools are provided to allow views to be kept up-to-date, and to allow views to be defined as functions of other (possibly changing) views. These tools promote sharing and enable the organization of files in ways that make it easier to identify information of interest than it is in existing systems. The prototype implementation has been used to organize information available from Internet archive sites; its directory service has been used from more than 7,500 systems in 29 countries. This paper discusses the goals of the Prospero File System, describes the prototype implementation, and discusses experience with the use of the system to date.