Abstract: Copper–indium–gallium–diselenide (CIGS) is a fast-evolving commercial solar cell. The firm demand for global carbon reduction and the rise of potential environmental threats necessitate spent CIGS solar cell recycling. In this paper, the sources and characteristics of valuable metals in spent CIGS solar cells were reviewed. The potential environmental impacts of CIGS, including service life, critical material, and material toxicity, were outlined. The main recovery methods of valuable metals in the various types of spent CIGS, including hydrometallurgy, pyrometallurgy, and comprehensive treatment processes, were compared and discussed. The mechanism of different recovery processes was summarized. The challenges faced by different recycling processes of spent CIGS were also covered in this review. Finally, the economic viability of the recycling process was assessed. The purpose of this review is to provide reasonable suggestions for the sustainable development of CIGS and the harmless disposal of spent CIGS.