Knowledge of the food and feeding habits of the western spotted frog has been primarily based on the reports of Tanner (1931), Fitch (1936), Schonberger (1945) and Moore and Strickland (1955). These analyses have all been purely qualitative in nature and based on collections made at one time during the spring or summer. The following study is based on an analysis of the contents of the digestive tracts of 178 individuals collected from populations in Yellowstone Park, Wyoming, during 1953, 1954, and 1955. Thirtyfive of these frogs were collected on August 17, 1953, about one-half mile northeast of Fishing Bridge along a backwater of the Yellowstone River. The remainder of the sample was collected in 1954 and 1955 from other populations near the north end of Yellowstone Lake. Because the sample represents all age groups and was collected gradually over the course of several seasons it has been possible to learn something of seasonal variation (both qualitative and quantitative) in the diet of the western spotted frog. Acknowledgment.-The writer wishes to acknowledge the role of members of the United States National Park Service in Yellowstone National Park, Wyoming, without whose cooperation this study could not have been carried out. Collection of materials was in accordance with a Class B permit. Appreciation is also expressed for use of facilities of the Museum of Vertebrate Zoology, and the Department of Zoology, University of California. In connection with the identification of materials recovered from the guts of frogs the writer wishes to gratefully acknowledge the assistance of the following persons: Dr. Paul D. Hurd, Jr., Assistant Entomologist, Department of Entomology and Parasitology, University of California, identified dipterans, hymenopterans, lepidopterans, and orthopterans (as well as certain representatives of other smaller groups); Hugh Leech of the California Academy of Science, identified both adult and larval beetles and certain other larvae,; Dr. Willis Gertsch of the American Museum of Natural History identified the spiders; Dr. Robert Usinger, Department of Entomology and Parasitology, University of California, and John Herring identified the hemipterans; Dr. Donald Denning of Velsicol Corporation identified the trichopterans; Dr. Edward L. Bousfield identified the amphipods; Ernest Roscoe identified the snails; and Helen Sharsmith of the University of California Herbarium identified certain plant remains. Finally, it is a pleasure to acknowledge the assistance and direction of Dr. Robert C. Stebbins in the preparation of this manuscript.