Foraminifera (unicellular organisms secreting a carbonate shell) are among the most important recorders of past environmental conditions. Examples of proxies are δ18O (for temperature and the waxing and waning of ice sheets), Mg/Ca for temperature, δ13C can be used as a measure for the strength of the biological pump and δ11B is a proxy for pH. However, the precision and accuracy of the recorded target parameter is often biased by a dependency of the proxy on additional variables. Species specificity, various vital effects, controlled by abiotic factors like light intensity, nutrient availability, carbonate chemistry, etc., but also by the life processes of the proxy carrier, such as respiration, calcification and photosynthesis of possible symbionts complicate their interpretation. Hence, proxy relationships are not as robust as one would like them to be. (In situ pressure) culture experiments (figs 2-5) and field studies in concert with numerical (cell) modelling and a thorough understanding of the biomineralisation processes (fig. 6) enable us to identify the mechanisms that control the primary relationship. This knowledge is required to develop robust proxy relationships for high quality paleoclimatic reconstructions.