  Interacting Binaries consist of a variety of stellar objects in different
stages of evolution and those containing accreting compact objects still
represent a major challenge to our understanding of not only close binary
evolution but also of the chemical evolution of the Galaxy. These end-points of
binary star evolution are ideal laboratories for the study of accretion and
outflow processes, and provide insight on matter under extreme physical
conditions. One of the key-questions of fundamental relevance is the nature of
SNIa progenitors. The study of accreting compact binary systems relies on
observations over the entire electromagnetic spectrum and we outline here those
unresolved questions for which access to the ultraviolet range is vital, as
they cannot be addressed by observations in any other spectral region.
