Leona Marshall Libby was a pioneer in modern climatic research, a field that gained great impetus in the late twentieth century because of the promise it holds for predicting future climatic trends. Libby’s work led to remarkable new procedures for investigating long-term changes in precipitation and temperature and thereby greatly expanding our knowledge of past climates. As Professor Rainer Berger writes in his foreword: “In recent years, tree ring–based temperature data have been collected which go far beyond the records available to historians. These data can be analyzed by Fourier transforms which identify certain periodicities. . . . Climatic changes detected by tree rings have been checked against historic records. . . . The correspondence is astonishing. . . . “At present weather forecasting is becoming more accurate for periods on the order of days, weeks, and months. Climatic prognoses have also been attempted for very long times of tens of thousands of years. But the intermediate range in the decades and centuries has so far been an enigma. It is here where tree ring thermometry plays its trump cards. “. . . Its potential is enormous in assessing worldwide crop yields, water inventory, heating requirements, stockpiling policies, and construction planning as well as political and military prospects.”