This lecture covers the pulse characteristics of X-ray free-electron lasers (XFELs), including pulse duration, duty cycle, and photon energy. It also discusses XFEL facilities around the world, such as LCLS, European XFEL, SwissFEL, and others. Furthermore, the lecture delves into the detailed architecture of XFELs, focusing on the electron gun, LINACs, bunch compressor, and low-emittance gun design.