  Binary/multiple status can affect stars at all stages of their lifetimes:
evolution onto the main sequence, properties on the main sequence, and
subsequent evolution. 5 $M_\odot$ stars have provided a wealth of information
about the binary properties fairly massive stars. The combination of cool
evolved primaries and hot secondaries in Cepheids (geriatric B stars) have
yielded detailed information about the distribution of mass ratios. and have
also provided a surprisingly high fraction of triple systems. Ground-based
radial velocity orbits combined with satellite data from Hubble, FUSE, IUE, and
Chandra are needed to provide full information about the systems, including the
masses. As a recent example, X-ray observations can identify low mass
companions which are young enough to be physical companions. Typically binary
status and properties (separation, eccentricity, mass ratio) determine whether
any stage of evolution takes an exotic form.
