  Type Ia SNe (SNe Ia) are thought to come from carbon-oxygen white dwarfs that
accrete mass from binary companions until they approach the Chandrasekhar
limit, ignite carbon, and undergo complete thermonuclear disruption. A survey
of the observed types of binaries that contain white dwarfs is presented. We
propose that certain systems that seem most promising as SN Ia progenitors
should be more intensively observed and modeled, to determine whether the white
dwarfs in these systems will be able to reach the Chandrasekhar limit. In view
of the number of promising single-degenerate systems and the dearth of
promising double-degenerate systems, we suspect that single-degenerates produce
most or perhaps all SNe Ia, while double-degenerates produce some or perhaps
none.
