The aim of this thesis is to examine the historical use of "poison cabinets", or restricted shelves, in Swedish libraries. Drawing upon the theories of Mary Douglas and Michel Foucault, it also seeks to sketch a cultural and ideological context of the practice; with the emphasis on social or mental hygiene, and disciplinary aspects. Through qualitative interviews as well as digitalized recordings of librarians active during the first half of the 20th century, actual examples of poison cabinets are presented. A closer examination is conducted of past collections at Lund University Library, and two large public libraries situated in Växjö and Sigtuna. The essay also investigates views on library censorship, controversial literature, and other related subjects reflected in th elibrary press during the period 1916-1979. In summary, the researched material suggests a historically widespread use of restricted collections, although the objectives of its use differ depending on library function. While the collection at Lund University Library appears to have been the result of state censorship, and is associated with the obligation to preserve materials imposed on legal deposit libraries, public libraries' poison cabinets have had a stronger connection to an educational reading culture. As such, public libraries' main concerns have been less about bad books, more about easy-to-corrupt patrons. The study is a two-year master's thesis in Library and Information Science written at Uppsala University.