The principal areas of utilization of thin films and coatings in the harnessing of solar energy are (1) t h e r m a l c o n t r o l o f s t r u c t u r e s, where reflecting or partially reflecting coatings and antireflection coatings are used to control incident solar radiation or to retain thermal energy; (2) p h o t o t h e r m a l c o n v e r s i o n where solar energy is converted to low grade heat (<150 °C) using reflector films, antireflection coatings, and selective solar absorber coatings; (3) = p i a i )=h o t o t h e r m a l/e l e c t r i c a l c o n v e r s i o n where solar energy is concentrated and converted to high‐grade heat which is used to power a turbine; and (4) p h o t o v o l t a i c c o n v e r s i o n where solar energy is converted directly into electrical energy using semiconductor films and junctions, transparent conductors, antireflection coatings, and metal electrode films. Films may be used in all of these areas for environmental protection. Several thin film systems have applications rather unique to solar energy. These include selective solar absorbers which have a high absorptivity for solar energy and a low emissivity in the ir, solar‐transparent electrical conductors such as tin oxide which are also good ir reflectors, and semiconductor films and junctions capable of efficiently converting solar energy into electrical energy (photovoltaic) or into chemical energy by photoelectrolysis. Selective solar absorber films may be selective due to interference effects, bulk properties, morphological properties, or a combination of effects. There are a number of ways to form selective solar absorbers, but oxide coatings formed by chemical conversion on steel or copper and electrodeposited black chrome (Cr/Cr2O3) coatings on steel or aluminum seem to be the most attractive for low temperature applications. Thermal oxides appear to be the most useful for high temperature applications. In thin photovoltaic systems the CdS/Cu2S system is the most widely considered. This thin film system may be formed by vacuum deposition, sputter deposition, or chemical spray techniques. Conversion efficiencies of 5%–6% are routinely obtained from vacuum deposited and chemically sprayed cells. Other thin film photovoltaic systems may give higher conversion efficiencies but at a greater cost per unit area. For many applications of thin films, high‐volume/low‐cost production, environmental stability, and material utilization are of great concern. Many thin film applications such as reflective coatings on glass, collectors for space heating, water heating, and absorption air conditioning are at present economically attractive and the potential thin film market is for 106–108 m2/yr. To make a meaningful impact on electrical generation capacity will require a fabrication rate of photothermal/electrical collectors of 2×108 m2/yr at a cost of $50–$150 per square meter (collector‐storage‐conversion‐power conditioning). To be economically feasible, the first collector surface (reflector or absorbing) must be low cost ($0.50–$5.00 per square meter). These costs, at the present time, are being achieved in the high‐volume tin electroplating industry and in the vacuum metallization of plastic sheet. By using concentration techniques, the cost of the final absorbing surface may be greater depending on the degree of concentration.