Eutectic freeze crystallization (EFC) is a treatment technology for saline streams that can recover both water and dissolved salts (or acids). It works by cooling the stream to the eutectic temperature, at which point both ice and salt (or acid) will crystallize. The ice, being less dense than the solution, floats, and the salt, being denser, will sink – thus effecting a gravity separation. Theoretically, EFC can result in zero liquid discharge (ZLD) and has several advantages over conventional separation techniques, including low energy consumption; high quality products and requires no additional chemicals. It can also be combined with other separation technologies to optimise separation processes. EFC can be applied to binary, ternary and multicomponent streams and thermodynamic modelling can be used to predict the eutectic temperature, eutectic composition, nucleation temperatures of ice and salt components, ice and salt recoveries and order of crystallization for crystal products. EFC is a classic coupled heat and mass transfer problem and, when operated as a continuous process, is suitable for the treatment of large volumes of saline streams. EFC has been developed from a laboratory curiosity to the point where commercialisation is currently under way.