The Max-Planck-Institute for Biogeochemistry, founded in 1997, is dedicated to the study of long-term interactions among the biosphere, atmosphere, geosphere and the oceans. Carbon, oxygen, hydrogen, and nitrogen - these four elements which are essential for life on earth - are continuously subject to biological, chemical and physical changes. Bound in varying chemical combinations, they are released together with other organic compounds by the biosphere and are tranported and distributed throughout the atmosphere and hydrosphere. Finally, they may find their way back to the biosphere to be converted again by various organisms. Since these transformations are interlinked and controlled by both the biology of the organisms as well as chemical and physical processes in the geosphere and atmosphere, they are known as the "biogeochemical cycles of the elements". The aim of research into biogeochemical cycles is to develop an understanding of the Earth System with all ist ecological implications, on a global scale. Processes on microclimate, landscape, ecosystem and global levels are closely interrelated and mutually influence each other. The trace gases carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapour (H2O) exemplify such interactions. Their concentration is regulated by biological, chemical and physical processes occuring in the terrestrial biosphere, in the oceans and in the atmosphere, and is also affected by planetary and human influences.