The fact that natural currents flow through the ground has been known for quite a long time. Some of these currents are local in character; some involve the whole of the earth's surface. These latter currents are called telluric currents. Their behavior and properties are outlined in general, and their usefulness for the practical purpose of geophysical exploration is discussed at length. In conclusion, an example of an actual survey by telluric currents on the Haynesville Salt Dome (Texas) is given, which illustrates the quality of the results which can be obtained in similar cases.