This paper analyses the character of usability criteria found in lists, which are used for interface design and evaluation. In order to understand usability criteria and relations between different criteria, a categorization of six usability criteria lists has been performed. The analysis has shown that the formulations of criteria reside on different abstraction levels. The results consist of two knowledge contribution. The first contribution is a hierarchical categorization model. The role of this multilevel abstraction hierarchy is to support practical problem solving processes by enabling and supporting the explicit articulation of criteria for a given context. The second contribution is a categorization of usability criteria. The aim of this categorization is to support the understanding of how different usability criteria relate (e.g. overlap or complement) to each other and highlight possible gaps.