Drilling deep into the earth holds a fascination for earth scientists derived in part from the fact that the drill hole is the ultimate test of a hypothesis. When surface exploration methods have been fully uti­ lized and all the geological inferences drawn about the structure be­ neath the surface, we must finally drill to sample directly the third dimension of the crust of the earth. The drill is thus the tool of choice of the energy and minerals re­ sources industry. Because of high cost, drilling has been only sparing­ ly used for solving fundamental problems in the earth sciences. But now, having used the quite sophisticated methodology of exploration geophysics, the exciting structural detail emerging from seismic re­ flection profiling in particular has led several nations to begin a major program of scientific drilling to solve some of the major prGb­ lems in the earth sciences. Hhat is described in this volume are the blueprints for national re­ search programs in France, the Federal Republic of Germany, Japan and the United States. The Soviet Union has already embarked on a major drilling effort, the results of which are soon to be published. Results, of course, are still few, and this first volume is more concerned with the problems to be solved.