Clumped isotope geochemistry is a new, dynamically developing field of research, which is based on the temperature-dependent clumping of the 13C and 18O isotopes within one molecule. Using the clumped isotope thermometer, the temperature of the carbonate precipitating fluids can be determined with high precision, based on solely the clumped isotope value (∆47) of carbonates. Besides palaeoclimatology, the method can be used in several research fields in geology, including palaeoceanography, atmospheric research, reservoir geology, geomorphology, structural geology, diagenesis, biogeochemistry, low temperature metamorphic processes, meteorite research, etc. Due to continuous developments, the number of applications is still significantly increasing. This paper briefly introduces the reader to the principles of clumped isotope geochemistry, reviewing its theoretical basis, its possible applications, available calibrations and reviews the current state of the art.