Experimental Tests of QED in Positronium: Recent Advances

The current experimental situation regarding tests of fundamental physics using positronium is reviewed. Five measurements are discussed and compared with theoretical predictions: the singlet and triplet annihilation decay rates, the ground state and the n = 2 energy intervals, and the Doppler-free two-photon excitation of the 1S to 2S transition. Previous results, recent progress (where appropriate), and the outlook for future improvements in these measurements are discussed.