In this book, we proposed velocity-free localization methods for acoustic and microseismic sources. This method does not require predetermination of wave velocity, which is a dynamically adjusted free real-time parameter. These methods solve the problem of large localization error caused by the difference between measured wave velocity and actual wave velocity in the source area and greatly improve the positioning accuracy. They are suitable for complex structures where the wave velocity changes dynamically in time and space, such as mines, bridges, buildings, pavements, loaded mechanical structures, dams, geothermal mining, oil extraction, and other engineering fields. This book includes progress in the development of localization methods, factors affecting the accuracy of source localization, analytical methods without the pre-measured wave velocity, velocity-free numerical methods for localizing acoustic sources, combined optimal velocity-free localization methods, velocity-free source localization considering complex paths of spatial structures, and theories as well as some cases of engineering applications of these methods.