This book reviews the HL-LHC experiments and the fourth-generation photon science experiments, discussing the latest radiation hardening techniques, optimization of device & process parameters using TCAD simulation tools, and the experimental characterization required to develop rad-hard Si detectors for x-ray induced surface damage and bulk damage by hadronic irradiation. Consisting of eleven chapters, it introduces various types of strip and pixel detector designs for the current upgrade, radiation, and dynamic range requirement of the experiments, and presents an overview of radiation detectors, especially Si detectors. It also describes the design of pixel detectors, experiments and characterization of Si detectors. The book is intended for researchers and master’s level students with an understanding of radiation detector physics. It provides a concept that uses TCAD simulation to optimize the electrical performance of the devices used in the harsh radiation environment of the colliders and at XFEL.