An HST Lensing Survey of X-ray Luminous Galaxy Clusters
 
 Graham Smith

 University of Durham
 
 We are conducting a lensing survey of 10 massive galaxy clusters at z~0.2
 using the Hubble Space Telescope.  These observations allow us to
 construct detailed models of the mass distribution in these systems at an
 epoch when growth of clusters is expected to be strong.  We also use
 multi-wavelength ground based observations to study the background
 galaxy populations and thus probe galaxy evolution to depths
 generally inaccessible to conventional surveys.  This talk will summarise
 the background to our survey and present our results to date, including
 constraints on the cluster dark matter profile from radial arcs, and a
 search for gravitationally lensed EROs.