  We introduce the class of intermediate mass binaries named Double Periodic
Variables (DPVs), characterized by orbital photometric variability (ellipsoidal
or eclipsing) in time scales of few days and a long photometric cycle lasting
roughly 33 times the orbital period. After a search conducted in the OGLE and
ASAS catalogues, we identified 114 of these systems in the Magellanic Clouds
and 11 in the Galaxy. We present results of our photometric and spectroscopic
campaigns on DPVs conducted during the last years, outlining their main
observational characteristics. We present convincing evidence supporting the
view that DPVs are semidetached interacting binaries with optically thick discs
around the gainer, that experience regular cycles of mass loss into the
interstellar medium. The mechanism regulating this long-term process still is
unknown but probably is related to relaxation cycles of the circumprimary disc.
A key observational fact is the modulation of the FWHM of HeI 5875 with the
long cycle in V393 Sco. The DPV evolution stage is investigated along with
their relationship to Algols and W Serpentid stars. We conclude that DPVs can
be used to test models of non-conservative binary evolution including the
formation of circumbinary discs.
