This volume is based on a meeting of researchers, forecasters, and users of La Niña forecasts, held at the U.S. National Center for Atmospheric Research in Boulder, Colorado. La Niña, the result of air-sea interaction, can briefly be described as the appearance of cooler than normal sea surface temperatures in the central and eastern equatorial Pacific Ocean that can affect global weather patterns. While people around the globe have become familiar with El Niño—a large scale warming of surface water that expands to cover the tropics—and its impacts, its counterpart, La Niña, is not so well known. Researchers at this La Niña Summit indicated that for many societies La Niña events can be as devastating as those of El Niño. The over riding purpose of the summit was to draw attention to the importance of improving our understanding of the La Niña phenomenon, identifying what is known, what is not yet known, and what societies need to know in order to prepare for La Niña’s impacts. La Niña and Its Impacts presents updated summit papers to introduce the reader to La Niña and offers a glimpse of the state of scientific knowledge about cold events and their impacts in developing as well as industrialized societies.