Active Galactic Nuclei in the Multi-messenger Era - Gamma-rays and Future

An exciting discovery made by space- and ground-based high-energy missions is the detection of gamma-rays from over 3,000 Active Galactic Nuclei.  Despite their intensive study, the location and origin of gamma-rays remain a mystery. The question of what powers gamma-ray flares is ultimately related to the energy dissipation and particle acceleration processes at work in relativistic jets, which is still an open question. In this talk, I will (1) present some exciting results of our recent study using multi-frequency and multi-messenger observations, (2) discuss the scientific potential of gamma-ray polarimetry, and (3) explore the scientific opportunities and wealth of information expected from the synergy of multi-wavelength polarimetry that will be brought to multi-messenger astronomy.