The history of solar cell development is briefly outlined, and the properties of the sun and solar radiation are reviewed. Properties of semiconductor materials that are important in the design and operation of solar cells are reviewed. The physical mechanisms involved in the generation and recombination of excess carriers are discussed and the basic equations of device physics are given. Both the dark and illuminated properties of p-n junctions are analyzed. Energy conversion efficiency limits are discussed for the photovoltaic process as well as the effects of various nonidealities on efficiency. Techniques for measuring the efficiency of photovoltaic devices are also described. The standard technology for making silicon solar cells is reviewed, and improved silicon cell technology is discussed. Considerations relevant to the detailed design of silicon cells are discussed. Several alternative device concepts are outlined and the structure and properties of solar cells made on some of the more developed alternatives to single-crystal silicon are discussed. Concentrating systems and photovoltaic systems components and applications are described. The design of stand-alone, residential, and centralized photovoltaic power systems are discussed. (LEW)