The purpose of the following account is to: (1) Show what kinds of chipmunks occur in Wyoming; (2) point out the interrelationships between these kinds; and (3) account, where possible, for the present distribution of these animals in Wyoming. METHODS, MATERIALS, AND ACKNOWLEDGMENTS Capitalized color terms in the following accounts are of Ridgway, "Color Standards and Color Nomenclature," Washington, D.C., 1912. The measurements of the skull that were used in this study were made as shown in White (1953:566, fig. 1). These are: Greatest length of skull, zygomatic breadth, cranial breadth, length of nasals, length of lower tooth-row, condylo-alveolar length of mandible, and inner mandibular length. Of the external measurements, only the total length and the length of the tail are recorded in table 1. Some field collectors measured the ear from the notch and others from the crown; most collectors measured the length of the hindfoot to the nearest millimeter rather than in tenths of a millimeter as would have been desirable. Consequently, I decided against using the length of the ear and hindfoot in this report. When the word "significantly" is used in comparisons, it is meant to show that there is a significant statistical difference between two or more samples. Whenever eight or more specimens from one locality were available, the mean, range, standard deviation, standard error of the mean, and coefficient of variability were calculated. Only adult specimens were used in comparison. "Aging" of specimens is discussed on page 587 of this paper. The geographic range of each species and subspecies is not described in writing, for, the localities are plotted on maps along with the geographic range of each subspecies, and under "specimens examined" the locality of each specimen or series of specimens is listed. In the synonymy of each subspecies there appears, first the first usage of a name, second the first usage of the name combination now employed, and third, pure synonyms. A total of 757 specimens of chipmunks are listed as examined in the course of preparing this report. Additional specimens were less carefully examined in the Biological Surveys Collection in Washington, D.C. Specimens used in my study, unless otherwise specified, are in the Museum of Natural History, University of Kansas. The symbols representing the collections containing specimens studied are as follows: BS--United States Biological Surveys Collection. FC--Collection of James S. Findley. MM--Museum of Zoology, University of Michigan. NM--United States National Museum. KU--Museum of Natural History, University of Kansas.