  We briefly review several activities at Mainz related to hadronic
light-by-light scattering (HLbL) using lattice QCD. First we present a
position-space approach to the HLbL contribution in the muon g-2, where we
focus on exploratory studies of the pion-pole contribution in a simple model
and the lepton loop in QED in the continuum and in infinite volume. The second
part describes a lattice calculation of the double-virtual pion transition form
factor F_{pi^0 gamma^* gamma^*}(q_1^2, q_2^2) in the spacelike region with
photon virtualities up to 1.5 GeV^2 which paves the way for a lattice
calculation of the pion-pole contribution to HLbL. The third topic involves
HLbL forward scattering amplitudes calculated in lattice QCD which can be
described, using dispersion relations (HLbL sum rules), by gamma^* gamma^* ->
hadrons fusion cross sections and then compared with phenomenological models.
