  Astronomical polarimetry is a powerful technique that can provide physical
information sometimes difficult or impossible to obtain by any other type of
observation. Almost every class of binary star can benefit from polarimetric
observations: pre-main-sequence objects, close or contact binaries,
mass-transfer systems, evolved binaries, cataclysmic variables, eclipsing
binaries, etc. In these systems, polarimetry can help determine the geometry of
the circumstellar or circumbinary matter distribution, yield information on
asymmetries and anisotropies, identify obscured sources, map starspots, detect
magnetic fields, and establish orbital parameters, to name just a few examples.
The orbital inclination in particular is a very important piece of information
for a binary system because it can lead to the determination of the components'
masses, the fundamental parameter that determines a star's initial structure
and subsequent evolution. This review will illustrate the usefulness of
polarimetric techniques for the study of binary stars, with examples of results
obtained for a variety of binary systems, and an overview of models, including
those used to retrieve the orbital inclination.
