The Fourth Symposium on Engineering Problems of Fusion Research was held at the US Naval Research Laboratory in Washington, D. C., 20–23 April, 1971. This was the fourth engineering symposium held in the United States since 1966. The purpose of these symposia is to present the engineering aspects of controlled fusion and serve as a meeting ground for the engineers working in the field. The Fourth Symposium was attended by approximately 90 engineers and scientists, representing the four major US Atomic Energy Commission laboratories, several universities, and a few industrial concerns. The Culham Laboratories in England and the Institute for Plasma Physics in Jülich, West Germany, were also represented. Fifty-eight papers were presented. The proceedings will be published by the IEEE Nuclear Science Group in the fall of 1971.