  The present knowledge of the structure of the photon is presented based on
results obtained by measurements of photon structure functions at e+e-
collider. Results are presented both for the QED structure of the photon as
well as for the hadronic structure, where the data are also compared to recent
parametrisations of the hadronic structure function F2gamma(x,Q^2). Prospects
of future photon structure function measurements, especially at an
International Linear Collider are outlined.
