AbstractUltra‐high‐dose rate “FLASH” radiotherapy (FLASH‐RT) has been shown to drastically reduce normal tissue toxicities while being as efficacious as conventional dose rate radiotherapy to treat tumors. A large number of preclinical studies describing this so‐called FLASH effect have led to the clinical translation of FLASH‐RT using ultra‐high‐dose rate electron and proton beams. Although the vast majority of radiation therapy treatments are delivered using X‐rays, few preclinical data using ultra‐high‐dose rate X‐ray irradiation have been published. This review focuses on different methods that can be used to generate ultra‐high‐dose rate X‐rays and their beam characteristics along with their effect on the biological tissues and the perspectives for the development of FLASH‐RT with X‐rays.