Good corrosion resistance to alkali metals and high-temperature strength make molybdenum a candidate material for controlled thermonuclear reactor structural applications. However, fabrication problems relating to its ductile-to-brittle transition behavior, notch sensitivity, oxidation rate, and susceptibility of welds to hot cracking have limited its use in the past. Procedures have recently been developed to fabricate molybdenum components for a complex chemical processing system. Closed-end -in.-o.d. containers up to 12 in. long were back extruded using ZrO2-coated plungers and dies, and blank preheat temperatures of 1600 to 1700°C. In cooperation with a commercial vendor, we found that ductile molybdenum tubing could be prepared by careful control of process variables and removal of contamination introduced during fabrication. By using either the gas tungsten-arc or the electron-beam process, complex components were fabricated by welding. Two important factors found to minimize weld hot cracking were stress relieving and preheating of components before welding. Radial compressive tests indicated glove-box welds were superior to field welds, but there was no correlation of weld properties with cleaning procedure or strain rate.