This book covers major techniques being used today to compute, analyze, visualize, and understand 3D electromagnetic fields in every major application of electrical geophysics. The 44 papers, written specially for this volume, are divided between techniques of 3D modeling and inversion (21 papers) and applications (23 papers). The latter include exploration for minerals and hydrocarbons, regional crustal studies, and environmental surveys. These contributions represent the work of 95 authors from 56 institutions in 13 countries around the world.