This book presents a systematic investigation into rock damage mechanics under multiphysics coupling, a critical field for deep earth resource exploitation and underground space utilization. It establishes a comprehensive theoretical framework that progresses from pure mechanical damage (MD) to complex thermo-hydro-mechanical -damage (THMD) coupling. The book details the development of advanced constitutive models, governing equations, and numerical solution strategies to describe rock failure under high stress, high temperature, and high pore pressure conditions. By integrating theoretical derivations with laboratory experiments and real-world case studies—such as rock thermal spalling, supercritical CO2 fracturing, and rock cycle thermal shock—the book provides practical guidance for predicting rock instability and optimizing engineering designs. It serves as a vital resource for researchers and engineers addressing the challenges of deep underground engineering.