Regional libraries in the Île-de-France region are open for 16.6 hours a week on average, with a maximum of 44 hours. Twenty-nine are open on Sundays and two are open seven days a week. What influence do opening hours have on which readers use libraries and how they use them? The MOTif, set up to observe the book sector in the Île-de-France region, has written a study examining reader profiles and use in conjunction with library opening hours. The study analysed six general reader categories (schoolchildren/students, highly qualified workers, workers with low qualifications, the unemployed, adults with children, and the retired) and six visiting times (evenings, Wednesdays, weekdays, Saturday mornings, Saturday afternoons, and Sundays). Should libraries open for longer, or target their opening hours better? Library use depends on what category the readers are in, while opening hours influence reader categories. Changing opening hours is thus one way of increasing visitor numbers. The study concludes with an account of opening hours at the Levallois-Perret multimedia library.