Its combination of good spatial resolution and soft X-ray sensitivity make Chandra an ideal instrument for the detection of luminous supersoft X-ray sources (SSSs)in external galaxies. M31 may provide the best opportunity to study a galactic population of SSSs. We have recently completed a survey of ~ 2560 square arcmin ( ~ 131 kpc^2) of M31, observing roughly half of this area on 2 or 3 separate occasions. We have discovered almost three dozen new SSSs, while revisiting many of the ROSAT-discovered SSSs. We find that, on time scales of months to years, SSSs are among the most highly variable X-ray sources. In fact approximately 80% of ROSAT-discovered sources were not detectable a decade later, or were on at a different level of activity. Sources discovered by Chandra were highly variable over the month to year time scales spanned by our observations. The spatial distribution of SSSs within M31 provides some surprising clues to their nature. We have used our data to refine estimates of the SSS population of M31 and explore the implications for the ionization of the interstellar medium and for the rate of Type Ia supernovae in spiral galaxies.