Abstract
Rapid variability is one of the main signatures of accretion onto compact objects, on scales from white dwarfs to supermassive black holes in AGN. Studies of these variations allows the dynamics of the accretion flow, structure of the accretion disk, spin of the compact object, and various oscillation modes to be probed in detail. Interacting binaries are ideal for this work because of their proximity and constrained geometry, but the variability timescales (for neutron stars and black holes) can be seconds or less. Hence this requires the new generation of giant telescopes (such as the GTC), combined with high efficiency, fast detectors in order to enter the new era of ``time domain astrophysics''.
