  The merger of two carbon-oxygen white dwarfs has long been theorized to lead
to a massive carbon-oxygen or oxygen-neon white dwarf, accretion-induced
collapse to a neutron star, or a type Ia supernova. Determining which mergers
lead to a particular outcome requires hydrodynamic simulations of the merging
process. I give a brief overview of the current understanding of mergers and
their end-products derived from simulations, and show how temperature, rather
than density or mass, most strongly determines a merging binary's subsequent
evolution. I then describe recent simulations that show mergers generate strong
magnetic fields that could help drive a merger remnant to ignition.
