This paper presents the results of a study in which "personas" are used for re-designing a digital library that is dedicated to the construction of Europe. In the first part of the paper, a definition is presented, along with issues associated with this method and in relation to other practical methods for gathering user requirements. In the second part, we evaluate the effects of personas in helping participants to generate ideas for the development of functions and services that would increase the usability and usefulness of the digital library. Five experts in human computer interactions and usability participated in this study. In the first phase of the experiment, they were invited to freely provide as many features and services as possible in order to increase the quality of the website. Then, in a second phase, they were invited to do the same thing, but this time with the help of 11?personas aimed at representing the target users of the digital library. To help them organize their ideas, participants were provided with a grid of seven functions (the "7?A?rule": Archive-Accredit-Analyze-Affirm-Associate-Actualize-Animate). These personas were designed and written without the participants and were validated with and by the project sponsors. The analysis of the results (quantitative and qualitative) showed that the use of personas increased the fluidity, flexibility, originality, and elaboration of ideas. Having descriptions (interests, needs, etc.) of fictitious users (even if they were built on the basis of actual and real data), seems to facilitate the generation of ideas of functionalities and services. We then discuss the questions and interpretations that designers raised in post-experimental interviews, and the biases introduced by the personas in terms of analogies and design constraints management. Finally, we discuss the complementarities of this method with other methods for generating ideas, the relevance and usefulness of ideas generated, its use by designers and discuss the capacity of this approach to improve the production of ideas.