  We derive dispersive representations for the anomalous process gamma pi -->
pi pi with the pi pi P-wave phase shift as input. We investigate how in this
framework the chiral anomaly can be extracted from a cross-section measurement
using all data up to 1 GeV, and discuss the importance of a precise
representation of the gamma pi --> pi pi amplitude for the hadronic
light-by-light contribution to the anomalous magnetic moment of the muon.
