The applications and requirements for thin film coatings in solar−thermal power systems are reviewed. The substantial impact of selective absorber coatings and antireflection coatings on both flat plate and concentrating type solar collectors is covered. The results of durability life tests on a high−temperature stable, vacuum−evaporated absorber coating consisting of layers of Al2O3−Mo−Al2O3 are reported. This coating was unaffected by 500 h at 930°C. Other tests included thermal cycling, thermal shock, ultraviolet irradiation, and solar wind simulation. An electroplated solar absorber coating for low−temperature applications (<200°C) has been developed which has a solar absorption of 0.96 and an infrared emittance of 0.07 at 100°C. A chemically etched antireflection coating for glass has been investigated. Solar transmission of 0.97 is possible with this low−cost technique.