Planktonic and benthic foraminifera reveal the state and the dynamics of the surface and deep ocean in the past. These protozoans are less than 1 millimetre in size. They occur in nearly all marine environments, from deep-sea trenches up to the salt marsh meadows. Even in brine channels of Antarctic sea ice they have been found. Many species respond sensitively to certain environmental conditions. Thus, the chemical and isotopic composition of their calcitic shell material records the properties of their ambient sea water. The texts also mirror metabolic and kinetic processes again which played a role in shell formation. Foraminiferen are mostly well-preserved in marine sediments, and they are found in great numbers. Therefore, foraminifera became the most important tool for paleoceanographic reconstructions.