While electronic learning environments provide exciting possibilities for supporting learners, the design of the user interface is as yet little understood. The purpose of this paper is to investigate the importance of specific usability attributes for online learning courses. A review of related papers on usability methods and learning theories is presented. The results of a usability study evaluating the use of a virtual learning environment providing distance learning for postgraduate studies in three Greek universities using WebCT, a well-known e-learning delivery platform, are presented. The review and the results of the study point towards specific usability attributes that need to be considered while designing usable learner-centered interfaces. (Contains 19 references.) (Author)