Multijunction solar cells produced by Spectrolab are the most efficient solar cells in the world, with a record efficiency of over 40%. Cell designs have been modified for high performance in concentrator photovoltaic (CPV) systems with the potential for low-cost, high-volume manufacturing. High-performance CPV cells have been designed, tested, and entered into production for field testing in CPV systems. Performance under variable concentrations and temperatures has been characterized and compared to semiconductor theory. The cell response has been applied to a spectral irradiance model to predict field performance at reference locations. Cell qualification has been completed for the current-generation C1MJ design.