In this talk I will show how the powerful combination of gravitational lensing and sensitive, high-resolution imaging can provide direct observational tests of galaxy formation scenarios under the cold dark matter paradigm as well as interesting constraints on cosmology.  In particular, I will discuss the following two subjects.

(1) Placing constraints on the Hubble Constant, curvature, and the dark energy equation of state parameter that are independent of and complementary to those obtained by other observational probes.  Even with a single gravitational lens system it is possible to obtain precisions on these measurements that are comparable to those obtained by the other methods.

(2) Placing observational constraints on the subhalo mass function by, for the first time, directly measuring masses of galaxy satellites outside of the Local Group.  These measurements can be made even if the satellites are composed purely of dark matter. The imaging used for these projects comes from Keck adaptive optics (AO) and Hubble Space Telescope (HST) observations.  In some cases the AO imaging is clearly sharper than that obtained with HST.