Finite Elements Model Updating (FEMU) is an advanced technique that has been applied for decades in Civil Engineering and used to improve the accuracy of Finite Elements Models (FEMs) by updating certain model parameters on the basis of experimental data. The application of this methodology to a FEM is crucial for ensuring that it represents, as accurately as possible, the true behavior of the structure and its materials under analysis. If these conditions are met, the updating process is concluded and the numerical model can be defined calibrated. Something to always keep in mind is that no matter how calibrated the model is, it will never behave exactly like the existing structure but its response and analysis can surely be useful to understand and predict the behavior of the structure.