Using Bragg-diffraction from perfect single crystals it becomes possible to split coherently, deviate about large angles and finally superimpose X-rays and thermal neutron beams in the same manner as has been possible for a long time with visible light. Interferometry with angstrom range radiation furnishes information about phases and amplitudes of scattered waves, the structure of defects in nearly perfect crystals, and- in the neutron case - about nuclear and magnetic scattering processes. Interferometric precision has thus become available on the very atomic scale. Literatur 1 U. Bonse, M. Hart: Appl. Phys. Lett. 6, 155 (1965). 2 H. Rauch, W. Treimer, U. Bonse: Phys. Lett. 47 A, 369 (1974). 3 W. Bauspiess, U. Bonse, H. Rauch, W. Treimer: Z. Physik 271, 177 (1974)., U. Bonse: Present State of X-ray Interferometry; in Proceedings of the 5th Int. Congr. on X-Ray Optics and Microanalysis, ed. by G. Mollenstedt und K. H. Gaukler (Springer: Berlin, Heidelberg, New York 1969) 1-10. 5 M. Hart: Rep. on Prog. Phys. 34,435 (1971). 6 M. Hart: Proc. R. Soc. A 346, 1 (1975). 7 U. Bonse, W. Graeff: X-Ray and Neutron Interferometry; in X-Ray Optics, ed. by H.J. Queisser (Springer: Berlin, Heidelberg, New York 1977) 93-143. 8 M. Ando, S. Hosoya: "An Attempt at X-Ray Phase Contrast Microscopy" in Proceedings of the Sixth Int. Conf. on X-Ray Optics and Microanalysis, ed. by G. Shinoda, K. Kohra and T. Ichinokawa (University of Tokyo Press 1972), pp.63-68.