There is much HCI-related literature on mental models and on the usability of digital libraries, however there is no previously published literature on users’ mental models of either traditional or digital libraries. This is surprising, since many digital libraries are difficult to use and it is not immediately clear why. Our study begins to fill this void by examining users’ mental models of traditional and digital libraries through a series of Contextual Inquiry interviews that mix traditional think-aloud observations, which usually demand minimal researcher intervention, and semi-structured interviews, which usually demand significant intervention. The study finds that participants’ mental models of traditional and digital libraries extend beyond surface similarities and differences, such as the hierarchical organisation of items in both types of library and the availability of documents in paper and electronic mediums. These models contain deeper similarities and differences based on the information-seeking goals that can be fulfilled by each type of library, issues concerning the contents and relevance of individual documents and entire libraries, and ‘how searching works’ and how to ‘troubleshoot’ in both types of library. Although the use of concrete analogies to influence users’ understanding or usage of digital libraries was not widespread, participants used their knowledge of Internet search engines to infer how searching might work in digital libraries. Additionally, most participants assumed that even if different at the interface level or at the level of the underlying technology employed, the search components of digital libraries, Internet search engines and other digital entities work in a similar way to bring back search results. The study also finds that a large component of users’ mental models of digital libraries is the notion of access restrictions. The insights gained from the observations relating to the above recurring themes in users’ mental models are discussed with a view of helping to improve digital library usability by reducing access restrictions and notifying users of any such restrictions upfront, by providing dynamic and context-dependent help to users, by carefully introducing analogies into the digital library interface (if and where appropriate) and by making multiple digital libraries searchable under a single front-end to enable them to be accessed, browsed and searched in the same way
