[en] Advances in the production and measurement of circularly polarized radiation at x-ray energies has proceeded slowly as compared to the visible portion of the electromagnetic spectrum. This is due, in large part, to the lack of birefringence exhibited by materials at short wavelengths (<1 Angstrom). However, as pointed out by Authier and experimentally demonstrated by Hart and Lang and Hattori, Kuriyama and Kato, birefringence does occur in perfect crystals under the condition of Bragg diffraction. Several groups have used this birefringence at the Bragg condition to produce operating phase plates at x-ray energies and it has been showed that a highly linearly polarized incident x-ray beam at 40 keV x-ray beam could be transformed via a silicon x-ray phase plate to a beam with a degree of circular polarization (P_C) of greater than 0.3. (A totally circularly polarized beam would have a P_C=1.) Calculations indicate, however, that considerable improvements can be achieved at high energies with different phase plate materials. A short introduction to the physics of x-ray phase plates will be presented along with a survey of the current status of x-ray phase development. Techniques for measuring the degree of circular polarization will also be discussed