Since the mid 19th century fossil fuel burning has released more than 250 billion tons of carbon in the form of CO2 into the atmosphere. Nearly 50% of the fossil fuel CO2 emitted into the atmosphere was subsequently taken up by the ocean, 80% of which is stored in the upper 200 m of the water column. While ocean uptake of anthropogenic CO2 provides an invaluable service by mitigating CO2-related global warming, it leads to a continuous acidification of surface ocean seawater. Unabated CO2 emissions will cause a doubling in surface ocean pCO2 levels over their pre-industrial values by the middle of this century, accompanied by a decrease in surface ocean pH three times greater than that experienced during the transition from glacial to interglacial periods. Ocean acidification and the related changes in seawater chemistry may directly impact marine organisms and ecosystems. Of particular importance is the reaction of calcifying organisms such as foraminifera, pteropods, corals, and coccolithophores. Here we will review what is know about organismal response to calcifying marine species with a special emphasis on coccolithophores.