Constant references to source material, which are characteristic of technical publications, are impractical in a book of this nature, for they spoil the continuity of the narrative. It would be unfair, however, not to give credit to the many fine archaeologists whose work has provided this knowledge, and it is desirable for the reader to know which publications to consult if he seeks more detailed information. Numbers in fine print which appear throughout the text refer to publications, listed under corresponding numbers in the bibliography, from which the information under consideration was derived. Although every effort has been made to avoid the use of unfamiliar terms, this has not always been possible. A glossary of technical terms will be found in the back of the book. The task of writing this book has been made a pleasant one by the fine cooperation of archaeologists and anthropologists. It is doubtful if the members of any other profession would have given more unstintingly of their time and have been more wholeheartedly willing to help and cooperate in every possible way. I am deeply indebted to Dr. Harold S. Colton, Dr. Edward T. Hall, Jr., Dr. Emil W. Haury, Dale S. King, Dr. Erik K. Reed, Charles Steen, Dr. Walter Taylor, and Dr. Ruth Underhill for checking and criticizing the manuscript or portions of it. Their suggestions have been of the greatest possible value. They are not, however, responsible in any way for any archaeological sins of commission or omission which may follow. I am most grateful to Earl H. Morris for graciously furnishing hitherto unpublished data on his excavation of Basketmaker houses and to Harold S. Gladwin and Emil W. Haury for permitting me to use information contained in personal letters. The kindness of F. H. Douglas, who put his excellent library at my disposal, is greatly appreciated. Without his assistance, and that of Marian Sheets who helped to assemble the necessary references, the work could never have been completed. My thanks are due to the American Museum of Natural History, the Arizona State Museum, Columbia University Press, Gila Pueblo, the Laboratory of Anthropology, Mesa Verde National Park, the Museum of Northern Arizona, the National Park Service, Peabody Museum of Harvard University, and the Taylor Museum for providing needed photographs. I am also very grateful to Gila Pueblo, the Laboratory of Anthropology, the Museum of Northern Arizona, and the Smithsonian Institution for permission to reproduce plates and figures from their publications.