  Optical spectropolarimetry and broadband polarimetry in other wavebands has
been a key to understanding many diverse aspects of AGN. In some cases
polarization is due to synchrotron radiation, and in other cases it's due to
scattering. Recognition of relativistically beamed optical synchrotron emission
by polarization was vital for understanding blazars (BL Lacs and Optically
Violently Variable quasars), both physically and geometrically. Radio
polarimetry of quiescent AGN is equally important, again for both purposes.
Scattering polarization was central to the Unified Model for Seyferts, Radio
Galaxies and (high ionization) Ultraluminous Infrared Galaxies. It provides a
periscope for viewing AGN from other directions. Finally, if we could
understand its message, polarization would also provide major insights
regarding the nature of the AGN "Featureless Continuum" and Broad (emission)
Line Region. I point out that high ionization ULIRGs have all the exact right
properties to be called Quasar 2s. Mid-IR observations generally don't
penetrate to the nucleus, greatly reducing their ability to diagnose the energy
source. In particular, LINER ULIRGs aren't necessarily starburst-dominated, as
has been claimed.
