Radiative Transfer for Polarized Radiation: a Personal, Historical Overview

Almost a century has elapsed since the first; application of spectro-polarimetry to the diagnostic of solar magnetic fields. Since then; dramatic progress has, been made in the instrumentation, which is now reaching unprecedented levels of sensitivity in the measurement of polarization signals in spectral lines. At the same time, the theoretical framework needed for the interpretation of polarimetric observations has steadily evolved from the pioneering methods based on simple formulae to a sophisticated structure which is nowadays used with success in the interpretation of solar observations. The present paper is intended to give a personal, historical perspective of the evolution of this research field and of its major achievements.