The recent revival of interest in the direct use of solar energy, which followed the 1973 oil crisis, has brought increased research and development activity in a number of areas. Some of these areas are discussed here, namely photocatalysis, photoelectrochemical cells, and photovoltaic devices. At the present time there is continuing research activity in photocatalysis for various purposes, including solar energy conversion, and there is also continuing research activity in photoelectrochemical methods. However, at the present time, photovoltaic devices are the only ones in limited terrestrial application for direct solar energy conversion into electricity.