Abstract
Usability evaluations inform user interaction design in a relevant manner, and successful user interaction design can be attained through usability evaluation. These are obvious conjectures about a mature usability engineering discipline. Unfortunately, research and practice suggest that, in reality, the interplay between usability evaluation and user interaction design is significantly more complex and too often far from optimal. This article provides a simple model of the interplay between usability evaluation and user interaction design that captures their main relationships. From the model, what is seen as the key challenges in improving the interplay between evaluation and design is outlined. The intention is to create a background against which the remainder of this special issue, containing5researcharticlespresenting empirical data on the interplay between design and evaluation and a commentary, can be contrasted.