  Below pion threshold virtual Compton scattering off the nucleon gives access
to the generalized electromagnetic polarizabilities. Different theoretical
results for the generalized polarizabilities have been compared. In particular,
the influence of the generalized polarizabilities on the unpolarized cross
section and on double polarization observables has been investigated.
Predictions for these observables have been obtained in the linear sigma model
and chiral perturbation theory.
