Additive manufacturing (AM), also known as 3D printing, is a technology that builds three-dimensional parts directly from computer-aided design (CAD) models by adding materials layer by layer. Unlike subtractive manufacturing, which removes material, AM allows the creation of complex geometries and materials that are not possible with traditional methods. Over the past two decades, significant progress has been made in AM technology, leading to numerous applications in aerospace, automotive, biomedical, and other fields. This review article discusses the main processes, materials, and applications of current AM technology and presents future research needs. The ASTM F42 Technical Committee defines AM as the process of joining materials to make objects from 3D model data, usually layer by layer. AM processes include stereolithography (SLA), fused deposition modeling (FDM), selective laser sintering (SLS), laminated objective manufacturing (LOM), three-dimensional printing (3DP), and laser metal deposition (LMD). These processes use various materials, including photo-curable resins, polyamides, wax, ABS, polycarbonate, metal/ceramic/polymer powders, and adhesive-coated sheets. AM technology allows the fabrication of complex parts without the need for special fixtures, significantly reducing lead time and being cost-effective for single parts and small batches. Over the past 20 years, AM has been applied in aerospace, automotive, biomedical, and other fields, evolving from prototype fabrication to rapid tooling and manufacturing. Current trends in AM include the direct fabrication of functional end-use products. Despite progress, challenges remain, including limited materials, poor part accuracy due to the "stair-stepping" effect, poor repeatability and consistency, and lack of standards. This paper reviews existing AM processes, their underlying techniques, commercial systems, materials, and applications in various fields. Future research needs of AM technology are also presented.Additive manufacturing (AM), also known as 3D printing, is a technology that builds three-dimensional parts directly from computer-aided design (CAD) models by adding materials layer by layer. Unlike subtractive manufacturing, which removes material, AM allows the creation of complex geometries and materials that are not possible with traditional methods. Over the past two decades, significant progress has been made in AM technology, leading to numerous applications in aerospace, automotive, biomedical, and other fields. This review article discusses the main processes, materials, and applications of current AM technology and presents future research needs. The ASTM F42 Technical Committee defines AM as the process of joining materials to make objects from 3D model data, usually layer by layer. AM processes include stereolithography (SLA), fused deposition modeling (FDM), selective laser sintering (SLS), laminated objective manufacturing (LOM), three-dimensional printing (3DP), and laser metal deposition (LMD). These processes use various materials, including photo-curable resins, polyamides, wax, ABS, polycarbonate, metal/ceramic/polymer powders, and adhesive-coated sheets. AM technology allows the fabrication of complex parts without the need for special fixtures, significantly reducing lead time and being cost-effective for single parts and small batches. Over the past 20 years, AM has been applied in aerospace, automotive, biomedical, and other fields, evolving from prototype fabrication to rapid tooling and manufacturing. Current trends in AM include the direct fabrication of functional end-use products. Despite progress, challenges remain, including limited materials, poor part accuracy due to the "stair-stepping" effect, poor repeatability and consistency, and lack of standards. This paper reviews existing AM processes, their underlying techniques, commercial systems, materials, and applications in various fields. Future research needs of AM technology are also presented.