Fundamental questions about our Universe, such as "How do stars and planets form?" and "How do galaxies evolve?", cannot be satisfactorily answered without understanding the role of astrophysical magnetic fields. Yet these magnetic fields remain notoriously difficult to measure. One of the few ways to probe magnetic fields in interstellar gas is through the polarized emission of molecular spectral lines. Molecular line polarization has proven to be a powerful tracer of magnetic fields, often in environments where no other magnetic field diagnostic is available. In this talk, I will take you on a journey through the many astrophysical applications of molecular line polarization. From revealing the magnetic fields in protoplanetary disks, stellar winds, and the disks surrounding active galactic nuclei--where few, if any, alternative tracers exist--, to modeling the polarized foregrounds of CMB experiments.
