Book excerpt: The income that supports the activities of the National Academy of Sciences (NAS) comes from two major sources: program revenue received from sponsors to pay for the myriad studies and other activities undertaken each year by the National Academies of Sciences, Engineering, and Medicine, and a much smaller sum that is obtained from our endowment under the endowment spending policies adopted by the Council. The goal of the endowment is to provide stable support for the Academy's programs and activities. To achieve this goal, the Council, acting on the recommendations of the Finance Committee, has historically authorized spending from the portfolio at a rate designed to maintain the purchasing power of the endowment over time. This Report of the Treasurer of the National Academy of Sciences presents the financial position and results of operations as well as a review of the endowment, trust, and other long-term investments portfolio activities of our Academy for the year ended December 31, 2017. While this book provides essential financial summary to key personnel, it also serves as a vital informative resource for various members of the public, private, and governmental sectors.