Spectro-polarimetry is an indispensable discipline of astrophysical research, despite its reputation as a highly specialized field. This is not surprising, as spectro-polarimetry is the gateway to investigating one of the most important ingredients in the physics of astrophysical plasmas: the magnetic field. The key role of magnetic fields in driving both the short- and long-term variability of the Sun and in triggering high-energy events, which may strongly impact our environment and society, is nowadays universally recognized.

The theoretical foundations of spectro-polarimetry are deeply rooted in the fundamental physics of the interactions of radiation with matter. Although progress can be slow and arduous, theoretical research in spectro-polarimetry is still very active, and new important contributions have recently come to light. At the same time, the numerical modeling of the generation and transfer of polarized radiation in realistic models of the solar atmosphere has become a very hot topic, calling for complementary competencies in physics and computational sciences. Certainly, spectro-polarimetric science is just as exciting on the instrumental side. New instruments for high-precision spectro-polarimetry are being developed for a new generation of ground-based solar telescopes, and a race to spectro-polarimetry from space has finally started, already succeeding with astonishing achievements. This volume covers all these topics, highlighting through reviews and specialized papers the progress and the most important results achieved in the field during the last few years.

The book is dedicated to the memory and work of one of the most eminent scientists in this field during the last decades, our mentor, colleague, and friend Egidio Landi Degl’Innocenti.