Ring lasers are commonly used as gyroscopes for aircraft navigation and attitude control. The largest ring lasers are sensitive enough that they can be used for high resolution inertial rotation sensing of the Earth in order to detect tiny perturbations to the Earth's rotation caused by earthquakes or global mass transport. This book describes the latest advances in the development of large ring lasers for applications in geodesy and geophysics using the most sensitive and stable devices available. Chapters cover our current knowledge of the physics of the laser gyroscope, how to acquire and analyse data from ring lasers, and what the potential applications are in the geosciences. It is a valuable reference for those working with ring lasers or using the data for applications in geodesy and geophysics; as well as researchers in laser physics, photonics and navigation.