Abstract: Flash butt welding, as a key technology for achieving seamless rail connections, has been widely adopted in global railway engineering due to its high efficiency and stable weld quality. In this paper, a systematic review of research progress on flash butt welding of railway track steels is provided, covering the welding processes and relevant technical standards for several typical rail materials, including pearlitic rail steel, high-manganese steel frogs, and bainitic rail steel. The influence mechanisms of key welding parameters—such as extension length, flashing process, and upsetting process—on the formability, microstructure, and service performance of welded joints are discussed. Furthermore, the formation mechanisms of typical welding defects, notably gray spots, and their detrimental effects on the service performance of welded joints are analyzed. Finally, in response to the increasing demands of high-speed and heavy-haul railway development on track performance, future research directions are outlined, emphasizing the necessity of developing advanced rail materials and optimizing welding processes.