These proceedings present a selection of invited and contributed papers presented during the 18th International Conference on X-Ray Lasers (the 18th ICXRL), held in Shanghai, China, from 17 to 21 July 2023. The conference is part of an ongoing series dedicated to recent developments in the science and technology of X-ray lasers and other coherent X-ray sources, with an additional focus on supporting technologies, instrumentation and applications. The book highlights advances in a wide range of fields including laser and discharge-pumped plasma X-ray lasers, the injection and seeding of X-ray amplifiers, high-order harmonic generation and ultrafast phenomena, X-ray free electron lasers, X-ray and gamma-ray generation, X-ray ghost imaging, optics and metrology, X-rays and γ-rays for fundamental science, the practical implementation of X-ray lasers, XFELs and super-intense lasers, and the applications and industrial uses of X-ray lasers.