In a geophysical survey energy is put into the ground and responses are measured. The responses depend upon the physical properties in the ground and the survey itself. The geophysical data can be used to generate images that convey geologic information and they can be further processed to yield information about the distribution of the physcial property. Geophysics is therefore useful if the connection between the geologic or engineering problem and the physical property is known. In this section we introduce some fundamental concepts and definitions about geophysical surveys, physical properties, terminology and provide examples that illustrate how geophysics can be used.