The basis for a study of the mammals of Washington was laid in 1929 by W. P. Taylor and W. T. Shaw in the "Provisional List of the Land Mammals of the state of Washington." Bailey's "Mammals and Life Zones of Oregon" and "The Recent Mammals of Idaho" by W. B. Davis deal with the habits and distribution of mammals in the areas bordering Washington on the south and east, and were very useful in the organization of the present report. The study was first planned from the taxonomic and ecologic point of view. Such a study, of necessity, involves the classification and distribution of the forms concerned. Classification has required more work than any other part of the study and has been, in a sense, the nucleus of the study. Nevertheless, as the report began to take form it was recognized that the part dealing with classification and other purely technical aspects of the paper probably would be uninteresting to the average reader. Therefore it was felt that a greater impetus to the study of the mammals of Washington would be given by reducing the taxonomic accounts to the minimum and dealing principally with the problems of distribution. As originally planned, the present report was to be of joint authorship by Dr. Victor B. Scheffer of the United States Fish and Wildlife Service, Seattle, and the writer. The press of other work prevented Dr. Scheffer from devoting as much time as he had planned to the project. He has, however, contributed his field notes, specimens, and photographs, and in many other ways assisted in the project. Field work on mammals of Washington was carried out by the writer from 1936 to 1940 but a decision to prepare a complete report was not reached until 1938. Intensive field work was done between 1938 and 1940. In August, 1941, the author took up residence at Berkeley, California. Drafting of the manuscript was begun at that time as a student under Professor E. Raymond Hall. War conditions and the press of other work delayed completion. Subsequently, the manuscript was put in final form at the University of Kansas.