Additive manufacturing (AM), widely recognized as 3D printing, has revolutionized prototyping and production on Earth, but its potential in extraterrestrial environments remains largely untapped. Zero-gravity additive manufacturing presents unique opportunities to fabricate critical components in orbit or on extraterrestrial bases, enabling self-sufficiency and reducing reliance on costly Earth-based supply chains. This paper explores the fundamental principles of material deposition in microgravity, examining how the absence of gravitational forces alters melt pool dynamics, solidification patterns, and layer adhesion. The integration of novel feedstocks, such as lunar regolith-based composites and metallic powders, further extends the applicability of AM beyond Earth. In addition to reviewing current experimental demonstrations on the International Space Station (ISS), this study outlines the engineering challenges of powder handling, thermal management, and structural reliability under space conditions. The work concludes by highlighting how zero-gravity manufacturing may transform space exploration, supporting long-duration missions and the establishment of sustainable habitats in orbit and on planetary surfaces.