A new AGU book, The North Atlantic Oscillation: Climatic Significance and Environmental Impact, edited by James W. Hurrell, Yochanan Kushnir, Geir Ottersen, and Martin Visbeck, investigates the current theories, models, and observations of the NAO and assesses future directions for research. The book is the first on this important phenomenon, the most prominent and recurring weather pattern over the Northern Hemisphere. In this issue, Eos talks with lead editor, James Hurrell. Hurrell is deputy section head of the Climate Analysis Section of the National Center for Atmospheric Research, where he has contributed to the International Panel on Climate Change assessments, and works with the international research program on climate variability and predictability.