  The analysis of the spatial distribution and kinematics of galaxies in
clusters allows one to determine the cluster internal dynamics. In this paper,
I review the state of the art of this topic. In particular, I summarize what we
have learned so far about galaxy orbits in clusters, and about the cluster mass
distribution. I then compare four methods that have recently been used in the
literature, by applying them to the same data-set. The results stress the
importance of reducing systematic besides random errors, for a reliable
determination of cluster mass profiles.
