  Clusters of galaxies contain a hot gas, which emits in X-rays. X-ray
telescopes such as XMM-Newton allow to study this plasma to obtain information
on physical quantities of these objects. We present here some results on the
total mass density distribution of clusters obtained with XMM-Newton based on
the hydrostatic approach. These results can be compared to models based on cold
dark matter. Generally good agreement is found between observations and models.
Furthermore we present a study on physical properties of a distant merging
cluster of galaxies, which demonstrates the potential of XMM-Newton studies on
this class of objects.
