Mayon is the most active Philippine volcano, having erupted 49 times since its ?rst recorded activity in 1616. Its gamut of eruptive behavior spans small but hazardous hydrovolcanic eruption (e.g. 1993), quiet lava effusion (e.g. 1993, 2006 and 2009) and explosive pyroclastic ?ow-forming (e.g. 1928, 1984, 2000-01) and deadly Plinian (e.g. 1814) eruptions. In the past two decades, a combination of seismic, geodetic, gas, hydrologic and visual observation techniques have been employed with variable successes. Nonetheless, constraining the long- to short-term behavior of Mayon’s magmatic system that contributes to highly precise eruption warning services remains a challenge.