Both of the earlier editions retain their value for students, but the criticism which may fairly be levelled at them is that Brown rarely contemplated the needs of a library of more than 40,000 volumes, and, therefore, omitted much that is necessary in the administration of such libraries. I have tried to balance this. It is perhaps desirable to set out the particulars in which the third edition differs from the second. The following chapters have been rewritten in their entirety: IV., V., VI., XV., XVIII., XX. and XXVII. The following are new: all Divisions I., XIII. and XIV.; and Chapters VII., XXVII., XXVIII., XXIX. and XXX. Everything else has been retouched, except the chapter on museums and art galleries; that I have left, because although the librarian ought to have a knowledge of curatorship, that knowledge is not library economy; and, within its limits, the chapter is good common sense. I have dealt drastically with the bibliographies, which consisted in the main of lists of articles in library periodicals. Every library student knows that textbooks and treatises are supplemented by periodical literature, and a reference to the indexes of library journals should be an obvious thing for him to make on any subject; and seeing that we have Cannons’s _Bibliography of Library Economy_, 1876-1909, for the years covered by the title, and that the best articles are now indexed in the Library Association Index, it seemed sufficient to make a general reference to Cannons and otherwise restrict the lists with few exceptions to separate publications. Appendix II, “The Librarian’s Library,” has been revised by Mr Richard Wright, M.C., to whom my thanks are due. An important omission is the Appendix of “Factors and Percentages,” which gave figures for calculating the size, cost, output, etc., of libraries. This has been deliberate; the conditions created by the War are so fluid that factors which are likely to have a permanent value are impossible to compile. Brown’s _Guide to Librarianship_ gives the pre-war factors, and it is unnecessary to reprint them here. The Memoir is based upon the obituary notices and appreciations which were collected and edited by Mr L. Stanley Jast for _The Library Association Record_, the biographical facts in particular being drawn from the memoir by Brown’s nephew, Mr James Douglas Stewart, which is included in those notices. Others will share my regret that his preoccupation with his new work at Manchester prevented Mr Jast from revising this _Manual_. I cannot but perceive, now that my work is finished, how much better it would have been had he filled my place. A few notes, prepared by Mr Jast for Chapters I.-II., have been included.