In this presentation I discuss current large surveys of galaxy clusters in the X-ray wavebands, with special emphasis on SPIDERS. It is one of the most ambitious observational programs aimed towards detecting, confirming, cataloguing and interpreting large samples (several thousands) of X-ray detected galaxy clusters, in an effort driven by precision cosmology and galaxy cluster population studies. I introduce some interesting scientific and technical challenges faced in this enterprise and I suggest ways of addressing them by taking examples originating from two wide-area, deep, XMM-Newton surveys: XMM-XXL and X-CLASS.