Well logging has come a long way from the simple electrical devices of the early years. Today's tools are much more diverse in their applications. Among these are tools which characterize geological properties of rocks in the borehole in a way that was previously only possible with oriented cores. Thus, borehole imaging, nuclear spectroscopy, nuclear magnetic resonance, and paleomagnetic logging provide precise information on bedding, mineralogy, texture and age of the rocks traversed by the borehole. Many of these logs can not only be acquired in the traditional "wireline" mode, but also in logging-while-drilling mode where the sensors are placed directly behind the drill bit, and the measurements are transmitted in real-time to the surface. Combined with new technology to drill deviated wells, the geoscientist now has tools which enable him to specify and develop reservoirs more accurately. This book is for researchers, graduate students and practising geoscientists.