High-order harmonic generation (HHG) in solids, the nonlinear upconversion of coherent radiation resulting from the interaction of a strong and short laser pulse with bulk matter, has come of age. Since the seminal experiments and theoretical developments, there has been a constant and vibrant interest in this topic. In this book, we invite experimental and theoretical experts in the field with the aim to summarize the progress made so far and propose new possibilities and prospects for the generation of high-order harmonics using solid samples. Nowadays, it is possible to engineer, both spatially and temporally with nanometric and attosecond resolution, the driven fields. This could bring solid HHG to the next exciting frontier as novel and fully tunable table-top coherent sources.