An active network is a computer network in which new protocols can be installed at run-time in any node within the network. For example, the deployment of Internet multicast technology has been slow because service providers have been reluctant to upgrade and reconfigure their routing nodes. Under the active network scheme, users who desire multicast services can have the service automatically installed without any direct intervention by the user or the provider. One major question in realizing active networks is how the code for the new active library can be found, or resolved, and retrieved. A model of the resolution and retrieval mechanisms is the major focus of this research. To validate the model, a proof-of-concept experimental system that realizes a simple active network architecture was developed. An active library resolution service model, suitable for a global Internet, was investigated using this experimental platform and a simulation system. The two protocol components that were built and studied are the active transport protocol and the active library resolution protocol. The experimental and simulation systems were used to evaluate the extensibility, overhead, resolution time, scalability, and policy constraint support of the service. Extensibility and policy constraint support are an integral part of the proposed design. For libraries located on servers that are at most ten hops away from the requesting source, the resolution time is under 2.6 seconds. Simulations of networks of different sizes and with different error rates exhibit linear resolution time and overhead characteristics, which indicates potential scalability. Behavior under high loss rates showed better than expected performance. The results indicate that the library resolution concept is feasible and that the proposed strategy is a good solution. / Ph. D.