Transition radiation is considered as a source of X-rays in the spectral range of 800 eV-10 keV. Both theoretical and experimental results for this region of the spectrum are presented. Medium energy (

< 100 MeV) and high-energy particle beams are used as sources for the production of transition radiation. The resonance effect, wherein there is in-phase addition between foil interfaces, is shown to be a method for bandwidth and frequency selection, and experimental results are presented. A favorable comparison is made to synchrotron radiation, and transition radiation is suggested as an X-ray source for lithography.