  We review the status of the hadronic light-by-light contribution to the muon
anomalous magnetic moment and critically compare recent calculations. We also
study in detail which momentum regions the pi^0 exchange main contribution
originates. We also argue that a_\mu^{light-by-light} = (11 \pm 4) \times
10^{-10} encompasses the present understanding of this contribution and comment
on some directions to improve on that.
