We have designed an interactive visualization framework for the automated trust negotiation (ATN) protocol and we have implemented a prototype of the visualizer in Java. This framework provides capabilities to perform the interactive visualization of an ATN session, display credentials and policies, analyze the relations of negotiated components, and refine access control policies and negotiation strategies. We give examples of the visualization of ATN sessions and demonstrate the interactive features of the visualizer for the incremental construction of a trust target graph (TTG). Our prototype, which implements most components of the visualization framework, has played a key role in a research project that has developed working trust negotiation systems in an industrial environment.