This research program covers three topics relating to the human-computer interface namely, voice recognition, tools and techniques for evaluation, and user and interface modeling. An investigation into the implementation of voice-recognition technologies examines how voice recognizers may be evaluated in commercial software. A prototype system was developed with the collaboration of FEMVIEW Ltd. (marketing a CAD package). A theoretical approach to evaluation leads to the hypothesis that human-computer interaction is affected by personality, influencing types of dialogue, preferred methods for providing helps, etc. A user model based on personality traits, or habitual-behavior patterns (HBP) is presented. Finally, a practical framework is provided for the evaluation of human-computer interfaces. It suggests that evaluation is an integral part of design and that the iterative use of evaluation techniques throughout the conceptualization, design, implementation and post-implementation stages will ensure systems that satisfy the needs of the users and fulfill the goal of usability.