  Interacting binaries containing white dwarfs can lead to a variety of
outcomes that range from powerful thermonuclear explosions, which are important
in the chemical evolution of galaxies and as cosmological distance estimators,
to strong sources of low frequency gravitational wave radiation, which makes
them ideal calibrators for the gravitational low-frequency wave detector LISA
mission. However, current theoretical evolution models still fail to explain
the observed properties of the known populations of white dwarfs in both
interacting and detached binaries. Major limitations are that the existing
population models have generally been developed to explain the properties of
sub-samples of these systems, occupying small volumes of the vast parameter
space, and that the observed samples are severely biased. The overarching goal
for the next decade is to assemble a large and homogeneous sample of white
dwarf binaries that spans the entire range of evolutionary states, to obtain
precise measurements of their physical properties, and to further develop the
theory to satisfactorily reproduce the properties of the entire population.
While ongoing and future all-sky high- and low-resolution optical spectroscopic
surveys allow us to enlarge the sample of these systems, high-resolution
ultraviolet spectroscopy is absolutely essential for the characterization of
the white dwarfs in these binaries. The Hubble Space Telescope is currently the
only facility that provides ultraviolet spectroscopy, and with its foreseeable
demise, planning the next ultraviolet mission is of utmost urgency.
