I discuss theory of hadronic contributions to the muon anomalous magnetic moment. The part associated with the light-by-light scattering for which there is no direct experimental input is the most challenging for theory. The hadronic description of the scattering amplitude is significantly improved by accounting for constraints from the short-distance QCD. It results in shifting the Standard Model prediction closer to the experimental value. A smaller hadronic contribution coming from electroweak corrections is also discussed briefly.