We present a new model of the lensing cluster of galaxies MS2137-23. By incorporating strong and weak lensing data in a fully elliptical lens modeling, we show that the total density profile must be close to the predictions of numerical simulations with an inner slope well consistent with a NFW profile. The model that best fits the lensing constraints is used to infer to line-of-sight velocity distribution (LOSVD) of stars in the central cD galaxy. This distribution is found to be far from Maxwellian. The important non-Gaussian tails produce a significant low-bias when measuring the velocity dispersion by assuming Gaussian absorption lines. In the case of MS2137, most of the information comes from multiples arcs. Internal kinematics of stars only help modeling the innermost kiloparsecs. However, in clusters with fewer constraints (no radial arcs for instance), a detailed modeling of both strong lensing and internal kinematics is crucial.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html