The phenomenon of diffraction has been widely used in research on atomic and atomic structure for last century . The lecture will outline the basic principles of diffraction using electromagnetic radiation ( X rays) or particles ( neutron). The lecture will also cover the basis for the extension to synchrotron radiation and outline the present developments of new sources of X rays such as the free electron lasers. Examples of leading edge experiments and comparisons between different techniques as well as current trends in instrumentation will
be included. A comparison between different techniques will be provided.