Polarized emission and absorption lines in core-collapse supernovae (CCSNe) trace detailed structures in the ejecta and circumstellar medium (CSM) that contain clues to the end stages of their progenitors’ lives as massive stars. Extracting this geometrical information, however, requires careful computational modeling that takes into account the aspherical distribution of the ejecta and CSM, as well as the potentially polarizing nature of line scattering. We present the results of such modeling for CCSNe with multi-epoch polarization observations obtained with the SPOL spectropolarimeter. In “interacting supernovae,” time-variable line polarization constrains the shape and density of the CSM, yielding valuable information about the progenitor’s late-stage mass loss episodes. In stripped-envelope supernovae, it provides new, quantitative evidence for the asymmetric nature of the explosions and the possible role of binary companions in shaping the supernova ejecta.