The article presents and describes in detail duplex steels used in modern sectors of industry (duplex, super duplex, lean duplex and hyper duplex), with particular attention paid to corrosion resistance and primary areas of application. The article also discusses welding-related issues including the preparation of the base material, welding techniques and procedures, requirements concerning heat input as well as pre-weld and post-weld heat treatment. The article emphasizes the growing use of duplex steels, among other things in welded structures, and forecasts their further development.