The distributed development and maintenance paradigm for component delivery is fraught with problems. One wants a relationship between developers and clients that is autonomous and anonymous. Yet components written in languages such as C++ require the recompilation of all dependent subsystems when a new version of a component is released. The design of Java?s binary format has side-stepped this constraint, removing the need for total recompilation with each change. But the potential is not fulfilled if programs have to be stopped to swap in each new component. This paper describes a framework that allows Java programs to be dynamically upgraded. Its key purpose is to allow libraries that are safe to replace existing libraries without adversely affecting running programs. The framework provides developers with a mechanism to release their libraries and provides clients with the surety of only upgrading when it is safe to do so.