In this investigation, the coefficients of thermal expansion of a number of crystals belonging to two structure types rutile and calcite have been studied by the x‐ray method with a view to correlating thermal expansion with crystal structure. The crystals studied areMgF2,ZnF2,NiF2,MnF2,CoF2,FeF2,SnO2,PbO2,TiO2(rutile),CrO2andRuO2belonging to the rutile type andCaCO3(calcite),CdCO3,ZnCO3,MgCO3,ScBO3andNaNO3belonging to the calcite type. The coefficients of thermal expansion have been evaluated from the precision lattice parameters determined with a Unicam 19 cm high temperature powder camera in the temperature range 30°C to 700°C. An attempt is made to correlate the variation in the coefficients of thermal expansion from crystal to crystal with the bond type, the interionic distances and the electronic configuration of the ions in the case of the rutile type compounds and with the ionic charge and the anion cation distance in the case of the calcite type compounds.