Leptonic Structure Functions of Photons

Virtual photons can fluctuate into diverse final states. This can be described in terms of structure functions for photons. Among other processes, such fluctuations can yield muon-pairs. Apart from supplying another test of QED, purely leptonic processes provide a calibration for the hadronic processes. We report on a measurement with single-tagged two photon events from the LEP experiment L3, at c.m.s. energies between 189 GeV and 206 GeV. An overview of the fundamental physical processes and a discussion of the structure function results will be presented.