The new European ARIANE 5 launcher being designed to put a payload mass of 6.8 t into geostationary transfer orbit is scheduled to be operational in 1995. It consists of a lower central stage with two solid propellant strap-on boosters and a single-engined storable propellant upper stage.The ARIANE 5 upper stage tank section has to be protected from the heat input of the hot engine nozzle during the 800 second firing period. Furthermore, the tank section and its components have to be thermally controlled for up to 3 hours after upper stage firing in order to maintain all equipment in an operational condition for possible passivation of the stage or re-ignition of the engine.This paper describes the thermal protection system development program with emphasis on the heat shield. The optimization process is shown starting with material selection combined with analysis and is followed by test verification. The foreseen manufacturing and integration approach is outlined as well.