This paper describes the usability testing of the Electronic Programme Guide (EPG) and some Interactive TV applications developed by Telefónica I+D for the Spanish satellite-TV operator Vía Digital. Fifty six people participated in the tests. In order to have a representative sample of the general population, participants were sampled following sex and age quotas from a total of 346 people randomly contacted by telephone. The paper also presents the results of the small telephone survey about TV viewing habits and the opinions about the advances in TV technology. The environment where the trials were made was a domestic setting, and people were asked to use a real working prototype, and to perform typical user tasks, as, e.g., searching for a particular program in the EPG. After each trial, the experimenter took note of the problems faced by the user, and whether the task was successfully completed, and then asked the subject to fill a short questionnaire about the usability of that particular application, including questions about difficulty, presentation speed and aesthetic appearance. At the end of the tests, subjects were also briefly interviewed to obtain the global opinion about the system, and including questions about some marketing issues of digital TV applications. Detailed results about the usability of the Programming Grid, and of the Theme and Channel Search functions are provided. After these results, design guidelines and user interface alternatives were produced, especially for the Programming Grid, which was considered by most subjects the most difficult part of the EPG. Two interactive TV applications, Tele-banking and Weather Channel, were also tested. These applications presented different difficulty levels for the users, and in particular, the two user interface approaches of the two interactive TV applications produced important differences in the usability of the system. Source: Article Abstract