Hadronic contributions to the photon vacuum polarization and their role in precision physics

I review recent evaluations of the hadronic contribution to the shift in the fine structure constant and to the anomalous magnetic moment of the muon. Substantial progress in a precise determination of these important observables is a consequence of substantially improved total cross section measurement by the BES II collaboration and an improved theoretical understanding. Prospects of further possible progress is discussed. (orig.)Available from TIB Hannover: RA 2999(01-028) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman