Zusammenfassung
We review the current status of theoretical calculations of the hadronic
light-by-light scattering contribution to the muon anomalous magnetic moment.
Different approaches and related issues such as OPE constraints and large
breaking of chiral symmetry are discussed. Combining results of different
models with educated guesses on the errors we come to the estimate \$\$a^\rm
HLbL=(10.52.6)10^-10.\$\$ The text is prepared as a contribution to
the Glasgow White Paper on the present status of the Muon Anomalous
Magnetic Moment.
Nutzer