The study of geomagnetism, particularly the study of the Earth's magnetic vield is of increasingly critical importance to geoscientists. Geomagnetism presents various aspects of the magnetic field of Earth. After an overview, topics covered include magnetospheric interactions, secular variation, magnetic induction, archeomagnetism, reversals, excursions, oceanic and continental magnetic anomalies, and long-term behaviors of the magnetic field. The mathematical techniques for treating these phenomena are discussed in detail. The electric and magnetic properties of Earth materials, as well as basic experimental and observational techniques are also described.