Hadronic light-by-light contribution to $(g-2)_mu$: a dispersive approach

After a brief introduction on ongoing experimental and theoretical activities on $(g-2)_mu$, we report on recent progress in approaching the calculation of the hadronic light-by-light contribution with dispersive methods. General properties of the four-point function of the electromagnetic current in QCD, its Lorentz decomposition and dispersive representation are discussed. On this basis a numerical estimate for the pion box contribution and its rescattering corrections is obtained. We conclude with an outlook for this approach to the calculation of hadronic light-by-light.