PrefaceIt is no wonder that Uncertainty Quantification has become more and more of an actuality in the last decade as the modelling capability jointly with computational power has increased a lot. In the past, the capability to predict flow field and performance in aero engines as well as in turbomachinery was of great support to the design. However, the range of errors in such results was so large as to suggest the use of CFD, mainly to understand the direction of trends and improvements more than the exact evaluation of thermo-fluid-dynamic parameters, which could affect performance, reliability and life of the engine components.Recently, we have seen two different but relevant matters: