The Mu2e collaboration will search for the coherent, neutrinoless conversion of muons into electrons in the field of a nucleus with a sensitivity improvement of approximately 10,000 over existing limits. Charged lepton flavor violation has never been seen.  We know that neutral leptons (neutrinos) change flavor, as do the quarks, and it is a mystery why the charged leptons have not shown their own transitions as well. The discovery potential of Mu2e confronts many popular BSM ideas, but Mu2e also probes new physics at a scale unavailable by direct searches at either present or planned high energy colliders. I will present the physics motivations for Mu2e, the experimental technique, and discuss potential upgrades.