One of the most important outstanding quests in cosmology is the understanding of the formation and evolution of galaxies and galaxy clusters. In particular, we seek to answer what the dark matter is, what are its properties, and how it shapes galaxies and galaxy clusters through cosmic time. Whereas the currently accepted paradigm for dark matter works well, discrepancies between model predictions and observations (such as the abundance of substructure in halos, and dark matter profile shapes) still remain. In this talk I will address these issues with gravitational lensing. In particular, I will show how I study the properties and the presence of (dark matter) substructure in galaxies, and how I use galaxy clusters as laboratories for dark matter. Further, using clusters as gravitational telescopes I will show some preliminary results of the search for highest redshift objects. The role of high resolution observations (HST now and SNAP in the future) is the key part of these projects and will shed the light on dark matter and high redshift galaxies, currently still part of the ``invisible'' Universe.