Other libraries belonging to specific organisations offer a specialised service to particular groups and are not always open to the public. Some of these libraries have a broad scope such as government department libraries and others operated by particular industries or commercial organisations which need access to their own information service. Trained librarians with experience select material for the library to purchase. They need a knowledge of publishers list, national bibliographies and reviewing journals. They should understand the needs of the library's users.
Cost is another factor to be considered in the selection of material.
Trained librarians catalogue and classify. They are well tutored in the rules and methods they use. A catalogue is the record of all the materials in the library. People use it to check whether the library has what they want. Classification is a way of coding all items in the library so that they can be arranged according to their subject matter.