Electron storage rings are in use or planned for use in the extension of radiometry into ranges of higher photon energies, from the visible spectral region continuously to the x-ray region up to photon energies of at least 100 keV. The storage rings serve as broadband primary standard sources for the development of a source-based radiometry and as sources of tuneable monochromatic photon fluxes for the development of a detector-based radiometry in combination with primary standard detectors. The state of the art is briefly summarized based on results obtained at the Berlin storage ring BESSY I (maximum electron energy 850 MeV), which was optimized for radiometry from the outset. Further progress in radiometry is expected at the future storage ring BESSY II (start of operation in 1998). At this third-generation storage ring (maximum electron energy 1,9 GeV) radiation from undulators, wigglers and wavelength shifters will be used for radiometry in addition to traditional synchrotron radiation from bending magnets. Furthermore, there are prospects at BESSY II to extend radiometry into the γ-ray range with photon energies in the MeV region by scattering laser and undulator photons at stored relativistic electrons.