From its first edition the purpose of Walford has been to identify and evaluate the widest possible range of reference materials. No rigid definition of reference is applied. In addition to the expected bibliographies, indexes, dictionaries, encyclopaedias, and directories, a number of important textbooks and manuals of general practice are included. While the majority of the items are books, Walford is a guide to reference material. Thus periodical articles, microforms, online and CD-ROM sources are all represented. In this volume a particular effort has been made to improve coverage of the latter two categories.