Active geophysical monitoring is an important new method for studying time-evolving structures and states in the tectonically active Earth's lithosphere. It is based on repeated time-lapse observations and interpretation of rock-induced changes in geophysical fields periodically excited by controlled sources. In this book, the results of strategic systematic development and the application of new technologies for active geophysical monitoring are presented. The authors demonstrate that active monitoring may drastically change solid Earth geophysics, through the acquisition of substantially new information, based on high accuracy and real-time observations. Active monitoring also provides new means for disaster mitigation, in conjunction with substantial international and interdisciplinary cooperation. This title offers an introduction of a new concept. It is written by most experienced authors in the field, with comprehensiveness.