A user-centered approach to interactive system development requires a way to represent the behavior of a user interacting with an interface. While a number of behavioral representation techniques exist, not all provide the capabilities necessary to support the interaction development process. The original goal of this research was to modify and extend the User Action Notation (UAN), a user- and task-centered behavioral representation technique. In order to facilitate and evaluate the improvement in the UAN, we developed and evaluated a taxonomic model of behavioral representation techniques. The development and evaluation of our model followed the epistemological cycle of observation, theorization, and evaluation. The model provides a framework for discussing, analyzing, extending, and comparing existing behavioral representation techniques, as well as being a springboard for developing and evaluating new techniques. / Ph. D.