The Twentieth Century can be looked back upon as a period in which a number of metal alloys unknown to previous centuries were introduced. Some were alloys in unusual combinations of previously-used metals, but also elements little used earlier. Some of these alloys have already had their day and exist now only in museum collections, where they may also present problems of preservation. Many metals lost their traditional applications or added entirely new ones. Elements such as uranium and the semimetals that had been of interest only to the ceramist at the start of the century are now the bases of industries unforeseen only a hundred years ago. From this it is concluded that predictions for the present century are uncertain.