  In this talk, I discuss recent developments concerning the possibility of
large extra spacetime dimensions. After briefly reviewing how such dimensions
can lower the fundamental GUT, Planck, and string scales, I then outline how
these scenarios lead to a new higher-dimensional seesaw mechanism for
generating neutrino oscillations --- perhaps even without neutrino masses. I
also discuss how extra dimensions lead to new mechanisms contributing to the
``invisibility'' of the QCD axion. This talk reports on work done in
collaboration with Emilian Dudas and Tony Gherghetta.
