In my talk I will first briefly review the application of galaxy clusters as tools to trace cosmic evolution. I will then discuss the recent advances in the this field, as driven by the increasing quality of observational data, and by the much improved description of clusters through detailed numerical simulations. I will present recent results on the analysis of such simulations aimed at calibrating clusters as precision tools for cosmology. In this context, I will discuss (a) possible biases that affect mass estimates based on X-ray and weak lensing data; (b) effects of baryons on the calibration of the halo mass function. I will finally discuss the perspectives for precision cosmology with galaxy clusters offered by the future generation of large multi-wavelegth surveys.