The authors desire to express their very, sincere thanks to Mr. F. B. Gilbreth for permission to use four of his photographs as illustrations, and to Mr. J. F. Butterworth, Mr. Gilbreth's general representative in England, for considerable assistance and helpful criticism. They are also glad to record their gratitude to Mr. H. W. Allingham, M. I. M. E., to whom they owe their introduction to Efficiency Methods, a good deal of information, and the opportunities they have had of seeing the system in operation, and (one of them) of working under it.Practically all the important books of reference on the subject are mentioned in the text. A Bibliography of books and magazine articles, up to 1914, will be found in C. Bertrand Thompson's collection of papers published under the title of "Scientific Management." This collection includes many original documents otherwise difficult to obtain, and forms an excellent historical sketch of the subject, considered as a movement. H. B Drury's "History and Criticism of Scientific Management" appeared in 1915, and was followed in 1916 by R. F. Hoxies "Scientific Management and Labour," for the most part very searching criticism.