Metal additive manufacturing (AM), also known as 3D printing, is a rapidly emerging technology that has the potential to revolutionize global parts manufacturing and logistics. It enables distributed manufacturing and on-demand production, reducing costs, energy consumption, and carbon footprint. This review discusses the state-of-the-art of metallic AM, covering material science, processes, and business considerations. It concludes that a paradigm shift is needed to fully exploit AM's potential. AM is defined as a process of joining materials layer by layer from 3D model data, as opposed to subtractive methods. It has been around for over two decades but has only recently emerged as a commercial technology. Key challenges include process control, sensor development, and modeling. AM requires real-time, closed-loop control systems to ensure quality and consistency. Additionally, new alloys must be developed to optimize properties. Metallic AM systems are categorized into powder bed, powder feed, and wire feed systems. Powder bed systems use a powder bed and energy source to melt or sinter the powder into the desired shape. Powder feed systems use a nozzle to convey powder onto the build surface, while wire feed systems use wire as feedstock. Each system has distinct advantages depending on the application. The metallurgy of AM involves complex thermal histories and repeated phase transformations. Ti-6Al-4V is the most extensively studied alloy, with high cooling rates reducing partitioning and favoring smaller grain sizes. However, AM alloys exhibit microstructural and mechanical property anisotropy, with the Z-direction generally being the weakest. Fatigue properties are dominated by processing defects such as micro-porosity and surface finish. Mechanical properties of AM alloys, such as Ti-6Al-4V and IN 625, are comparable to conventionally fabricated materials. However, AM alloys can exhibit anisotropy in yield and tensile strength. Fatigue life is influenced by surface finish, with smoother surfaces showing longer fatigue life. HIP processing can enhance properties by closing porosity. Qualification and certification of AM components are critical for widespread adoption. Current processes are too costly and time-consuming, necessitating technological alternatives for accelerated qualification. Business considerations include fixed and recurring costs, with AM being favored in small production lots where higher material costs are offset by reduced fixed costs. AM has the potential to reduce environmental impact through design optimization and reduced material waste. However, further research is needed to fully assess its environmental impact. A systems approach spanning the entire life cycle of AM components is required to capture true benefits and potential pitfalls. In summary, AM is a transformative technology with significant potential in manufacturing, logistics, and environmental sustainability. However, challenges in qualification, certification, and environmental impact require continued research and development.Metal additive manufacturing (AM), also known as 3D printing, is a rapidly emerging technology that has the potential to revolutionize global parts manufacturing and logistics. It enables distributed manufacturing and on-demand production, reducing costs, energy consumption, and carbon footprint. This review discusses the state-of-the-art of metallic AM, covering material science, processes, and business considerations. It concludes that a paradigm shift is needed to fully exploit AM's potential. AM is defined as a process of joining materials layer by layer from 3D model data, as opposed to subtractive methods. It has been around for over two decades but has only recently emerged as a commercial technology. Key challenges include process control, sensor development, and modeling. AM requires real-time, closed-loop control systems to ensure quality and consistency. Additionally, new alloys must be developed to optimize properties. Metallic AM systems are categorized into powder bed, powder feed, and wire feed systems. Powder bed systems use a powder bed and energy source to melt or sinter the powder into the desired shape. Powder feed systems use a nozzle to convey powder onto the build surface, while wire feed systems use wire as feedstock. Each system has distinct advantages depending on the application. The metallurgy of AM involves complex thermal histories and repeated phase transformations. Ti-6Al-4V is the most extensively studied alloy, with high cooling rates reducing partitioning and favoring smaller grain sizes. However, AM alloys exhibit microstructural and mechanical property anisotropy, with the Z-direction generally being the weakest. Fatigue properties are dominated by processing defects such as micro-porosity and surface finish. Mechanical properties of AM alloys, such as Ti-6Al-4V and IN 625, are comparable to conventionally fabricated materials. However, AM alloys can exhibit anisotropy in yield and tensile strength. Fatigue life is influenced by surface finish, with smoother surfaces showing longer fatigue life. HIP processing can enhance properties by closing porosity. Qualification and certification of AM components are critical for widespread adoption. Current processes are too costly and time-consuming, necessitating technological alternatives for accelerated qualification. Business considerations include fixed and recurring costs, with AM being favored in small production lots where higher material costs are offset by reduced fixed costs. AM has the potential to reduce environmental impact through design optimization and reduced material waste. However, further research is needed to fully assess its environmental impact. A systems approach spanning the entire life cycle of AM components is required to capture true benefits and potential pitfalls. In summary, AM is a transformative technology with significant potential in manufacturing, logistics, and environmental sustainability. However, challenges in qualification, certification, and environmental impact require continued research and development.