This book is concerned with time-dependency in rock mechanics and rock engineering, whose spectrum is very wide. While the term "time-dependency" involves time-dependent behavior/rate-dependent behavior of rocks in a conventional sense, this books attempts to cover the spectrum as much as possible including coupled processes of thermal, hydrological and diffusions in rocks. It presents theoretical formulations, experiments, numerical formulation and examples of applications. Of paramount concern is the long-term response and stability of rock engineering structures, including for instance man-made and natural slopes and underground facilities such as tunnels and powerhouses.