In the coming years, several astronomical surveys will scan the night sky with regular cadence, revealing an enormous number of supernovae and other optical transients, many never seen before. The study of these stellar disruptions is not only a vibrant topic in itself, but also impacts fundamental questions in cosmology, nucleosynthesis, compact objects, and the sources of gravitational waves.  Insight from theory and modeling is required to physically interpret this data and to explain the new phenomena discovered.  Here I discuss recent advances in large scale radiation hydrodynamical simulations which are predicting the signatures of a diverse range of explosive transients.  I focus first on the thermonuclear, or Type Ia, supernovae.  Using multi-dimensional light curve models, I show how variations in Type Ia brightness are driven by deviations from spherical symmetry, and illuminate the physical origin of the empirical correlations used to standardize these supernovae as measures of cosmic expansion.   I then present predictions for two very different sorts of transients:  the disruption of extremely massive stars via the electron-positron pair instability (believed to characterize the death of the first generation of stars) and the faint optical emission from the merger of neutron stars (considered a promising source for gravitational wave observatories).