Photovoltaic energy conversion has demonstrated remarkable improvements in performance over the past 60 years. The rate of solar cell efficiency change has actually increased over the past 20 years as researchers have moved beyond elemental semiconductors to increasingly more sophisticated materials and devices. In addition, significant improvements in materials quality and deposition technology have further fueled this dramatic improvement in device performance. Diversifying from silicon to III-V compound semiconductor materials has enabled the development of multijunction solar cells with 3, 4, and even 6 subcells to achieve ever higher conversion efficiency. For 1-sun space application(s), these III-V multijunction cells are demonstrating, similar to 35% efficiency, while under terrestrial concentrated sunlight conditions efficiencies are >42%. This Article will discuss the development of high efficiency III-V multijunction solar cells, focusing on recently developed metamorphic device structures and novel lattice matched approaches.