Water gas shift (WGS) is a key process in chemical industry in order to increase the hydrogen concentration in the feeding stream in the reactors for the synthesis of some of the most important bulk chemicals (ammonia, methanol and hydrocarbons by Fischer-Tropsch synthesis). WGS has become a fundamental reaction in all the biomass to liquid (BTL) processes using syngas produced by biomass gasification. Even if this technology is well known, its industrial application has not been fully exploited yet. Several research activities are on going in order to improve the catalytic systems involved in high and low temperature WGS reactors and the whole process. This review aims to describe the main traditional catalytic systems able to promote this reaction and the most recent advance in the field. Thermodynamic and kinetics of WGS are critically discussed, with the goal of briefly identifying the fundamental and practical features of the process.