Gravity and magnetic data are among the oldest geophysical data acquired for the purpose of resource exploration and exploitation. They currently also have the widest areal coverage on the Earth, span a great range of scales, and play important roles in mineral, energy, groundwater, and environmental clear-up arenas. 3D inversion techniques have emerged as a major tool for the quantitative interpretation of these data. The availability of 3D inversion techniques has advanced potential- field interpretation from 'anomaly bump hunting' to 3Dimaging of the subsurface by reconstructing the distribution of density or magnetic properties in various geological units and, thereby, have shifted interpretations from the data domain to the model domain. Similarly, inversion techniques are also poised to make major contributions to integrated modeling and interpretation, as well as to differentiating and characterizing geology, geological processes, and reservoir dynamics. The purpose of this book and the accompanying course is to present selected inversion-based interpretation techniques in the fields of mineral and oil & gas exploration and production. The focuses are twofold. The first is on inversions and associated techniques in support of such quantitative interpretation of gravity and magnetic data. The second is on the applications of these techniques in mineral exploration andreservoir monitoring.