ABSTRACT. Engineers are continuously called to build simplified models of intricate problems and phenomena. They traditionally apply the so-called Simplified Physics Approach to build models and codify them. Wind Engineers often employ Proper Orthogonal Decomposition (POD), also in the wake of the referential works of Giovanni Solari. The so-called Reduced Order Models (ROMs) include the above and many other approaches. ROMs are useful to provide a deep insight into huge amount of experimental data harvested from wind tunnel tests or computational simulations, and/or surrogate expensive high-fidelity models in uncertainty quantification, optimization or design-oriented applications. The lecture provides a wide rigorous general modelling framework, and discuss the past, present and future applications in bluff body aerodynamics and wind engineering.