Intended as an introductory guide for non-specialist readers, this book describes the historical importance of the Earth's magnetic field and its role in protecting the planet from harmful high-energy radiation from the Sun. With explanations of underlying physics of processes and references to original scientific works, the reader can explore the Earth's magnetic field and the various ways in which geomagnetics are used and measured, including the analysis of modern satellite-based investigations and the effects of solar activity on the geomagnetic field.