This paper describes a usability study performed on three different e-encyclopaedias, all of which were available on the web, contained similar content and targeted similar audiences, but differed in their styles of presentation. The purpose of the study was to discover the effectiveness of each design in terms of overall usability and subjective satisfaction, to extract general guidelines for the successful design of e-encyclopaedias, and to examine the requirements of different user groups. Keywords electronic encyclopaedias, e-encyclopaedias, usability, evaluation