Polarized light provides key information on the physical conditions and geometry of astrophysical plasmas otherwise unattainable via conventional spectroscopy. In particular, the remote sensing of solar and stellar magnetic fields requires the measurement and rigorous theoretical interpretation of polarization signals in atomic and molecular lines, which are induced by various subtle physical mechanisms. I will begin presenting a brief introduction to ``Astrophysical Spectropolarimetry'', emphasizing the importance of developing diagnostic tools that take proper account of the Zeeman Effect, optical pumping processes and the Hanle Effect. Only in this way may we hope to investigate the strength and topology of stellar magnetic fields in a parameter domain which ranges from at least milligauss to many thousands of gauss. In the second part of the talk I will discuss some interesting applications in solar magnetism, suggesting also what type of collaborations between physicists and chemists could lead to new advances in astrophysics.