The concept of an x-ray microscope in which the enlarging element consists of a pair of conicoidal mirrors is well established. Although the geometrical principles were published in 1952,' microscope manufacture did not seriously commence until the mid-I970s, stimulated primarily by the need to examine the x-ray emissions from laser fusion targets? The potential value of the x-ray microscope as a tool for studying the microstructure of materials, complementing optical and electron microscopes, was well understood in the 1950s; the reason for the long delay in exploiting it was that the manufacturing tolerances required were beyond thencurrent manufacturing capabilities. This is still the case, in that the ultimate resolution of a microscope is limited by manufacturing errors and not by the aberrations of the optical instrument. At the National Physical Laboratory (NPL), a considerable effort has been devoted to acquiring an understanding of the details of the microscope optical design in order to be able both to evaluate the potential performance of the microscope and to specify the manufacturing tolerances. The tolerances are so severe for high resolution microscopes that all the manufacturing stages must be undertaken at a very high level of technology. Areas to which particular attention is being paid include the choice of microscope materials, manufacturing methods, and metrology. The progress to date of each is discussed in this paper. Special high brightness microfocus x-ray sources are being developed that, besides acting as a source for the microscope, can also be employed to produce high resolution microradiographs with a much greater field of view than an imaging system and, with the addition of an electron beam scanning system, be used to evaluate the performance of imaging systems. A high gain, double channel plate image intensifier has been developed to enable visual observations to be made of the enlarged image. Direct observation facilitates the setting up of the microscope and provides a rapid method for selecting the area of interest in the specimen.