Prof. Hiram Bingham's explorations in South America, 1906-1911, and particularly his discoveries in 1911, were so important that when he was seeking funds for another Peruvian expedition in 1912, the Research Committee of the National Geographic Society made him a grant of $10,000, Yale University contributing an equal amount. His preliminary report to the National Geographic Society and Yale University of the work done in 1912 is printed herewith and forms one of the most remarkable stories of exploration in South America in the past 50 years. The members of the Society are extremely gratified at the splendid record which Dr. Bingham and all the members of the expedition have made, and as we study the 250 marvelous pictures which are printed with this report, we also are thrilled by the wonders and mystery of Machu Picchu. What an extraordinary people the builders of Machu Picchu must have been to have constructed, without steel implements, and using only stone hammers and wedges, the wonderful city of refuge on the mountain top. Gilbert H. Grosvenor, Editor