The actor model of concurrent computation unifies the functional and object-oriented programming language paradigms. The model provides a flexible basis for concurrent programming. It supports local state, dynamic creation and configuration, and inherent parallelism. Because of the fluidity of actors, specifying and debugging actor systems is often considered difficult. We believe visual programming techniques are of fundamental importance in addressing powerful concurrent systems of this nature. Not surprisingly, a number of methods to visualize actor programs have been proposed. We give an outline of visualization techniques and their relation to actors. We then discuss one such proposal, namely the use of Predicate Transition nets, to visualize actor programs.