A library is an organized (using a classification system) collection of books and other print and nonprint materials. Library contents and materials vary according to the patrons or clientele being served. Library searches used to be done through the card catalog, a record of the collection’s materials. Most libraries, in the late twentieth century, switched their records (under the same classification systems) to computers, so that users can access information in various databases. Libraries’ vast collections of materials can be obtained by such methods as going to the shelf and finding a desired book, requesting a book (many libraries do not allow patrons to access books directly), making a computer printout, or asking for a book through interlibrary loan. Libraries are vital organizations in modern global societies. They house not only books but also other resources, including periodicals, newspapers, audiovisual materials and various other print and nonprint information. Librarians provide a variety of services to a clientele used to a service oriented, computer-age society. The Internet has enabled individuals to reach libraries across nations and to acquire information instantaneously. The roles of libraries and librarians have become more complex and challenging, especially in issues of selection and censorship.