Duplex stainless steels are two-phase alloys based on the iron-chromium-nickel system. Duplex stainless steels offer corrosion resistance and cost advantages over the common austenitic stainless steels. Although there are some problems with welding duplex alloys, considerable progress has been made in defining the correct parameters and chemistry modifications for achieving sound welds. This chapter provides a basic understanding of the development, grade designations, microstructure, properties, and general welding considerations of duplex stainless steel. It also discusses the influence of ferrite-austenite balance on corrosion resistance and the influence of different welding conditions on various material properties of alloy 2205 (UNS...