  A microscopic coupled-channels model for Compton and pion scattering off the
nucleon is introduced which is applicable at the lowest energies
(polarizabilities) as well as at GeV energies. To introduce the model first the
conventional K-matrix approach is discussed to extend this in a following
chapter to the "Dressed K-Matrix" model. The latter approach restores
causality, or analyticity, of the amplitude to a large extent. In particular,
crossing symmetry, gauge invariance and unitarity are satisfied. The extent of
violation of analyticity (causality) is used as an expansion parameter.
