Additive manufacturing has the potential to positively affect human spaceflight operations by enabling the in-orbit manufacture of replacement parts and tools, which could reduce logistics requirements for the International Space Station and future long-duration human space missions. Additive manufacturing can also help to reimagine a space architecture that is not constrained by the design and manufacturing confines of gravity, current manufacturing processes, and launch-related structural stresses. This report evaluates the prospects of in-space additive manufacturing, examines technologies available and in development, and considers possible impacts for crewed space operations and robotic spacecraft operations. According to the report, the International Space Station provides an excellent opportunity for civilian and military research on additive manufacturing technology. This report makes recommendations for future research, suggests objectives for an additive manufacturing roadmap, and envisions opportunities for cooperation and joint development.