This paper aims to review the progress in cement clinker chemistry since the last International Conference on the Chemistry of Cement in 2011.Although Portland cement clinker is still, by far, the most important compound of modem cements we show that there is a strong development of alternatives.This is mainly due to the emission of carbon dioxide during the calcination of calcium carbonate as raw material whose reduction is the goal of international activity due to anthropologically caused climate change.Furthermore, it is an objective to use both more raw materials that are located close to the concrete plants and alternative fuels.Developments in the field of cement clinker chemistry show a potential for alternatives.Thereby we discuss both old and new ideas.But it has been shown that the substitution of Portland cement clinker has to consider not only reduction in CO2 emission during fabrication: For practical solutions the performance in both in terms of strength development and durability has to be adequate compared to the ordinary Portland cement clinker.