This volume presents a coherent and detailed description of the field, and brings together leaders in theoretical research. The book discusses today's state-of-the-art, as well as tomorrow's tools: the supercell-pseudopotential method, the GW formalism, Quantum Monte Carlo, learn-on-the-fly molecular dynamics, finite-temperature treatments and more. A wealth of applications are included, from point defects to wafer bonding or the propagation of dislocation.