Gravitational lensing phenomena are widespread in electromagnetic astrophysics, and in principle may also be uncovered with gravitational waves. We examine gravitational-wave events in the limit of Geometric Optics, where we expect to see multiple signals from the same event with different arrival times and amplitudes, and Wave Optics, where we expect to see effects such as interference and diffraction. I will review existing results and discuss several exciting opportunities for gravitational-wave lensing, which may uncover hidden objects and structures, and open new windows in fundamental physics and astrophysics.