Applied geophysics uses a large number of methods to investigate the subsurface. Because of its ability to produce images down to depths of thousands of metres with a resolution of tens of metres, the seismic method has become by far the most commonly used geophysical method in the oil and gas industry. In the past 20 years, the quality of seismic information has been greatly improved by the use of 3-D seismic methods. However, extracting useful information from seismic images remains the interpreter's craft skill, in which elements of geological and geophysical knowledge are combined in varying proportions. This book is intended for people beginning to develop that skill, either as part of a University course or at the beginning of a career in the oil and gas industry. It assumes that the reader has some general background knowledge of the seismic method. There are several excellent texts that cover the whole range of theory and practice (for example, R. E. Sheriff & L. P. Geldart, Exploration Seismology (2nd edn, 1995), Cambridge University Press). Our intention is not to replace these volumes, but rather to concentrate on the techniques of interpretation that are specific to 3-D seismic, or are greatly improved in usefulness by applying them to 3-D datasets (such as amplitude studies, AVO analysis, inversion and time-lapse seismic). However, there is enough explanation of the underlying principles to make the book fairly self-contained. In particular, the acquisition and processing of 3-D seismic data are described in some detail.