The number counts of galaxy clusters are a powerful and independent cosmological probe. We review how several challenges in this experiment can be overcome by a combination of multi-wavelength data and hydrodynamical simulations. Specifically we will discuss how to empirically constrain the incompleteness and contamination fraction of cluster samples. We will also present an innovative method to quantify the accuracy of weak gravitational lensing inferred masses, as well as recent applications of this method. In the end, we will look ahead, to the opportunities and challenges present by future and starting cosmological surveys like eROSITA, Euclid and CMB stage 4.
Marco De Petris