This study is designed to be followed by a similar study of two typical groups of ruins, viz, that of Canyon de Chelly, in northeastern Arizona, and that of the Chaco Canyon, of New Mexico; but it has been necessary for the writer to make occasional reference to these ruins in the present paper, both in the discussion of general arrangement and characteristic ground plans, embodied in Chapters II and III and in the comparison by constructional details treated in Chapter IV, in order to define clearly the relations of the various features of pueblo architecture. They belong to the same pueblo system illustrated by the villages of Tusayan and Cibola, and with the Canyon de Chelly group there is even some trace of traditional connection, as is set forth by Mr. Stephen in Chapter I. The more detailed studies of these ruins, to be published later, together with the material embodied in the present paper, will, it is thought, furnish a record of the principal characteristics of an important type of primitive architecture, which, under the influence of the arid environment of the southwestern plateaus, has developed from the rude lodge into the many-storied house of rectangular rooms. Indications of some of the steps of this development are traceable even in the architecture of the present day. The pueblo of Zuñi was surveyed by the writer in the autumn of 1881 with a view to procuring the necessary data for the construction of a large-scale model of this pueblo. For this reason the work afforded a record of external features only. The modern pueblos of Tusayan were similarly surveyed in the following season (1882-’83), the plans being supplemented by photographs, from which many of the illustrations accompanying this paper have been drawn. The ruin of Awatubi was also included in the work of this season. In the autumn of 1885 many of the ruined pueblos of Tusayan were surveyed and examined. It was during this season’s work that the details of the kiva construction, embodied in the last chapter of this paper, were studied, together with interior details of the dwellings. It was in the latter part of this season that the farming pueblos of Cibola were surveyed and photographed. The Tusayan farming pueblo of Moen-kopi and a number of the ruins in the province were surveyed and studied in the early part of the season of 1887-’88, the latter portion of which season was principally devoted to an examination of the Chaco ruins in New Mexico. In the prosecution of the field work above outlined the author has been greatly indebted to the efficient assistance and hearty cooperation of Mr. Cosmos Mindeleff, by whom nearly all the pueblos illustrated, with the exception of Zuñi, have been surveyed and platted.