Over the last decade, additive manufacturing (AM) has witnessed significant adoption due to its efficiency and cost-effectiveness. This chapter focuses on the economic and environmental benefits of AM, particularly in metal additive manufacturing (MAM). MAM's precise layer-by-layer deposition of metallic materials offers advantages such as lightweight designs and customized components. However, achieving the desired mechanical properties in MAM presents challenges related to complex microstructure formation influenced by various factors. The integration of MAM with Industry 4.0, characterized by digital technology incorporation, holds promise. Industry 4.0 enables real-time process monitoring and control, enhancing productivity, quality assurance, and resource management. Digital twin concepts facilitate simulation and optimization. This chapter emphasizes sheet lamination, directed energy deposition, and powder bed fusion, with cyclic phase transitions impacting material properties. Metal AM methods like powder bed fusion (PBF) and directed energy deposition (DED) are discussed. Sheet-based AM processes retain localized energy sources and offer versatility. Metal AM holds potential for in-space manufacturing (ISM), reducing reliance on Earth-launched parts during space missions. The overview highlights the significance of AM, particularly in MAM, within Industry 4.0, sheet-based processes, and ISM while addressing challenges and opportunities in efficient metal part production.