The development of optical interferometry will literally open a new dimension in the study of binary stars. As a prelude to the session, this paper reviews those properties of stars in binary systems that are of greatest scientific interest and summarizes what has been learned with the traditional tools of photometry and spectroscopy. We then discuss the information provided by interferometry and how it is most powerfully exploited in combination with other, complementary tools. This is illustrated by a few recent cases in which optical interferometry has helped to break new ground in ways that point towards the future. Finally, some recommended procedures are listed which may help to optimize the scientific returns of interferometric studies of binary stars.