Technical and experimental developments of large scale facilities now enable research experimenters to follow, in real time and in situ, the structural changes that may occur in a material, crystal, glass or liquid at different temperatures, pressures and times. These developments result from improved sources of radiation (synchrotron, neutron sources) and detection systems and, also by miniaturization of the heating devices. This chapter will be devoted to some examples of applications for the study of glass-ceramics and the crystallisation mechanisms based on measures by X-ray absorption spectroscopy and diffrac- tion of X-ray and neutrons.