The paper describes austenitic-ferritic or duplex stainless steels in technical terms and gives reasons why they are such good alternatives to traditional austenitic grades of the 300-series for the construction of desalination plants. Duplex grades possess the same, or even better, corrosion resistance as their austenitic counterparts and they have higher strength, at least twice that of the austenitic grades, enabling gauge, weight and cost reductions. The paper also describes a number of applications within desalination, both membrane and distillation processes, where the advantages of duplex stainless steels have been utilized. Four major engineering companies involved in thermal desalination have realised that duplex stainless steel is a cost effective alternative to traditional materials for such plants. It also describes some applications from other industrial sectors showing that desalination is not a type of guinea-pig industry; it has rather been very slow to adopt the concept with duplex stainless steels.