The possibilities and advantages of synchrotron radiation (SR) techniques (X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), anomalous scattering) are demonstrated on diverse examples. It is shown that SR methods allow the attainment of new information about solid state reactions. High intensity X-rays were used to study the structure of the reaction zone for topochemical transformations and the kinetics of phase formation in solid-solid and sol-gel processes in situ.