Manufacturing or repairing parts on-site, high geometric freedom, and feedstock efficiency have long been regarded as nascent capabilities of additive manufacturing (AM) technologies. Researchers aim to adopt these capabilities for the future of space exploration, and polymer AM demonstrations in space were achieved in 2014; however, methods to process metals and other materials are needed. This paper provides a comprehensive review of AM research tested on reduced-gravity platforms from academia and industry across the globe. In addition, complementary processes and technologies under development are summarized. Reports from the literature are categorized by established AM process terminology and processed material. Lastly, alternatives to enabling metal AM in space are discussed, and knowledge gaps are presented.