The British Rail Class 317 is an electric multiple unit (EMU) passenger train constructed by British Rail Engineering Limited in two batches, 48 sets being produced in 1981–82 and 24 sets in 1985–87. They were the first of several classes of British Rail EMU to be based on the all-steel Mark 3 bodyshell, departing from the "PEP"-aluminium design which had spawned the earlier Class 313 to Class 315, Class 507 and Class 508. The Mark 3 bodyshell was also the basis of Class 318, Class 455, and the diesel Class 150. The Class 317 uses overhead alternating current electrification.