This thesis is based on an investigation to find out in what way 40 Swedish public libraries keep and preserve their library materials. The investigation is based on inquiries sent out to the libraries. It deals with the keeping of books with regard to external factors which have destructive effects on library materials as well as the safety at the library buildings. It is, as well, about the preserving work being done at the libraries. Comparisons are made with literature and accounts about preserving measures and recommendations regarding appropriate environment in premises and depositories. The results show great differences between the libraries as to the library environment, i.e. from paying attention to the factors and taking measures to taking no measures at all. The safety concerning theft and fire varies as well. Most of the libraries have old and/or special collections. Nearly all the libraries do simple repairing themselves, while over half the number, in addition, apply to special firms for binding or more advanced restoring work. Topicality, currency and the last volume are essential criteria of book preservation. There is an urgency to preserve local collections and valuable old materials as well.