Alfa Romeo had commissioned Bertone to design the Giulietta SS for racing, but this was unsuitable as it was too heavy and handled badly. Franco Scaglione was asked to design the SZ on the Giulietta SS chassis and contracted Zagato to build using their aluminium expertise. About 200 of the original 'Coda Tonda' (round-tailed) SZ were made before Ercole Spada at Zagato developed the more aerodynamic SZ2 'Coda Tronca' with Kamm tail. Some 30 SZ2 cars were made.