In 1936, prior to the second world war, and again in 1942 during the war, the American Society for Testing Materials conducted symposia on industrial radiography. These symposia were published by the Society in book form. Both the holding of the symposia and publishing information about the techniques and fields of application did much to build up industrial radiography practice as an important factor in the mobilization of American industry for national defense. After the war there was a widespread expectation that industrial radiography and other associated methods of nondestructive testing would lapse into a minor, routine rôle in our industrial production. Actually the postwar years have brought a great decrease in routine finished-product inspection, but at the same time there has been a fascinating surge forward in two other aspects of this still young and vital technology. These rapidly developing aspects are in the engineering of radically new equipment and in the skilled exploitation of non-destructive testing in the management of engineering and material-processing development projects. In both cases the progress that has been made led the Society to undertake sponsorship of symposia that would be followed by publication. Two symposia were held at the Annual Meeting in 1949, one on Radiography and one on Ultrasonic Testing, and a further symposium on the management and economic aspects of non-destructive testing is scheduled for the Annual Meeting in 1950. In the present volume, covering the 1949 symposium, three papers deal with progress in the development and application of electrostatic and betatron-type X-ray generators operating at potentials above the familiar one million volt range. These machines make available to industry not only penetration of steel up to 16 in. in thickness but also the ability to observe the internal structure of engineering parts and assemblies with a sharpness and precision resulting from a very small X-ray source and great freedom from fogging by X-ray scatter.