The depreciation problem is one of live importance. It has recently attracted much attention on the part of accountants and engineers interested in the solution of problems of a financial character. Although the litera ture on the subject is constantly growing in volume, it is often difficult for the student to secure a good knowl edge of the fundamentals of the subject because of the form which most of the recent discussions have taken. Almost all of the material on the subject is in the form of magazine articles. Usually the writer of such an article fails to cover the field fully, preferring to expand on some point in which he is especially interested. It is needless to say that this lecture does not cover in detail all phases of the matter. On the contrary, in the attempt to cover the essential features of the problem it has been necessary to omit referring to many things of secondary importance/ It is believed, however, that this lecture covers the most important features of the prob lem, and if an interest in the subject and a fair under standing of its leading features is acquired by the student its purpose will have been fulfilled.