SiO 2 coatings have been applied to Incoloy 800H samples by two methods, namely plasma-assisted vapour deposition (PAVD) and laser fusion. The corrosion resistance of the coatings was assessed in oxidizing, sulphidizing and carburizing environments. Thin (20 μm or less) amorphous SiO 2 layers produced by the PAVD process provided excellent protection to attack in all these environments at temperatures,up to about 900°C. At higher temperatures, however, increasing recrystalization of the coating resulted in failure. Thicker coatings (50–200 μm) produced by the laser fusion of oxide crystallites are still at an early stage of development. Mixed coatings of SiO 2 and Cr 2O 3 were formed as a consequence of oxidation processes during coating, and initial tests have given encouraging results in sulphidizing and oxidizing environments.