The _dictionary_ catalogue is the form most popular here and in America, and, unfortunately, is usually the most defective. As its name implies, it resembles the ordinary alphabetical arrangement of the dictionary, and embraces in one alphabet entries of authors, subjects, titles, and series. The principle of subject entry is that books are entered under the specific subject, and not usually under broad headings; thus books on Trees are entered under that word, and not, as in a classified catalogue, under their historical, or logical, place in Botany. The dictionary form is that most attractive to the general reader, and in its ideal form is a remarkably effective instrument; that is to say, when it analyses the subjects in books, and links all specific and general headings by cross-references. The best examples are the Brooklyn _Library Catalogue_ and the _Index Catalogue_ of the U.S. Surgeon-General’s Library; and good English examples, which will repay study, are the catalogues of Bishopsgate Institute, London, and of Hampstead Public Libraries which seems to be modelled on the Bishopsgate catalogue. Objections to the dictionary catalogue are that it gives no connected view of any subject and of its collateral subjects, that it is rarely cross-referenced adequately, that headings are chosen haphazard, and, what is its chief objection, if it is printed it is out-of-date the day after publication--an objection which does not apply so much to the printed classified catalogue, as that lends itself to publication, and to revision, a class at a time. Librarians using this form should base their subject entries upon the _A. L. A. List of Subject Headings_ (second edition, 1912) or the _Library of Congress List_ (in progress, issued in parts by the Library), as these will secure a choice of recognized headings and save much labour in deciding between alternative headings. The application of the Library of Congress list may be studied in The Library Association _Index to Periodicals_ (1915-16), which is, in the main, arranged upon it.