Cataclysmic Variable StarsThe study of cataclysmic variables interacting binary stars containing a white dwarf accreting from an orbiting companion is undergoing an exciting renaissance, as it embraces observations at all wavelengths. Cataclysmic variables allow, in particular, the direct and detailed study of equilibrium and non equilibrium accretion discs; in turn these developments also help in our understanding of X ray binaries, black holes and active galactic nuclei.