  Strong lensing is a powerful tool to address three major astrophysical
issues: understanding the spatial distribution of mass at kpc and sub-kpc
scale, where baryons and dark matter interact to shape galaxies as we see them;
determining the overall geometry, content, and kinematics of the universe;
studying distant galaxies, black holes, and active nuclei that are too small or
too faint to be resolved or detected with current instrumentation. After
summarizing strong gravitational lensing fundamentals, I present a selection of
recent important results. I conclude by discussing the exciting prospects of
strong gravitational lensing in the next decade.
