Although research and practice have shown that the success of a usability engineering program depends on the identification and correction of usability problems, these problems remain an underutilized source of information. Insufficient guidance regarding the capture of usability problem data results in the loss of information during the problem reporting phase as problem reports are often vague, imprecise, and incomplete. In addition, the absence of a framework for understanding, comparing, categorizing, and analyzing those problems, and their relationship to development context, not only constrains product improvement, but hampers efforts to improve the user interface development process. A new taxonomic model (the Usability Problem Taxonomy) is presented which contributes to both product and process improvement. The Usability Problem Taxonomy (UPT) is used to classify and organize usability problems detected on interactive software development projects. Individual UPT categories are associated with two aspects of development context: developer roles and skills, and development activities, methods, and techniques. Two studies were conducted during the course of this research. The first study showed that the UPT can be used to classify usability problems reliably. Findings indicated that level of agreement among classifiers (beyond chance agreement) was statistically significant. Findings in the second study led to the identification of roles and activities that address individual UPT categories as well as those that do not. Procedures for using the UPT in both product and process improvement are outlined. Examples are presented that illustrate how the UPT can be used to generate higher quality problem descriptions and to group those problem descriptions prior to prioritization and correction. In addition, steps that guide developers in diagnosing weaknesses in the current user interface development process are enumerated. Possible improvement strategies are presented that focus on the selection of specific development activities and team members appropriate for a given project. / Ph. D.