This paper presents two empirical usability studies based on techniques from Human-Computer Interaction HCI and software engineering, which were used to elicitate requirements for the design of a hypertext generation system. Here we will discuss the ndings of these studies, which were used to motivate the choice of adaptivity techniques. The results showed dependencies between di erent ways to adapt the explanation content and the document length and formatting. Therefore, the system's architecture had to be modi ed to cope with this requirement. In addition, the system had to be made adaptable, as well as adaptive, in order to satisfy the elicitated users' preferences.