This volume includes revised versions of most of the presentations made at the International Conference Understanding the Earth Sys tem: Compartments, Processes and Interactions" held on November 24-26, 1999 in Bonn. The Conference was organized by the German National Committee on Global Change Research as part of the Bonn Science Festival 1999-2000. The Bonn Science Festival (Wissen schaftsfestival Region Bonn) was organized and funded by sfg Strukturforderungsgesellschaft Bonn/Rhein-Siegl Ahrweiler mbH. The generous support for organizing the conference and printing this volume by sfg is...