Book excerpt: Polar ice cores have provided tremendous advances in our knowledge of past climate change. They also contain an archive of geochemical data, which can certainly delineate some of the forcing factors that govern climate change. However, our ability to interpret these data is severely curtailed by lack of knowledge of the processes governing the transfer of chemical species from the air to the snow. This book outlines the potential and problems of ice core chemistry and discusses the processes involved in air-snow transfer. It gives the state of current knowledge and an agenda for future research.