The free-electron laser (FEL) FLASH (short for Free-Electron Laser in Hamburg) has been in operation since 2000. It has a length of 315 m. It is based on a test facility for superconducting accelerator technology built in 1997 for the TESLA project and has served as a user facility for experiments with the generated FEL radiation since 2005. FLASH provides ultrashort light pulses in the extreme ultraviolet and soft X-ray range for seven experimental stations and is also used as a test facility for the development of accelerator and FEL technologies.