This volume is based on papers presented at the International Symposium on X-Ray Microscopy held at Brookhaven National Laboratory, Upton NY, August 31-September 4, 1987. Previous recent symposia on the sub ject were held in New York in 1979, Gottingen in 1983 and Taipei in 1986. Developments in x-ray microscopy continue at a rapid pace, with im portant advances in all major areas: x-ray sources, optics and components, and microscopes and imaging systems. Taken as a whole, the work pre sented here emphasizes three major directions: (a) improvements in the capability and image-quality of x-ray microscopy, expressed principally in systems attached to large, high-brightness x-ray sources; (b) greater access to x-ray microscopy, expressed chiefly in systems employing small, often pulsed, x-ray sources; and (c) increased rate of exploration of applications of x-ray microscopy. The number of papers presented at the symposium has roughly dou bled compared with that of its predecessors. While we are delighted at this growth as a manifestation of vitality and rapid growth of the field, we did have to ask the authors to limit the length of their papers and to submit them in camera-ready form. We thank the authors for their con tributions and for their efforts in adhering to the guidelines on manuscript preparation.