  There are obvious and direct ways in which the presence of binary companions
may affect activity in OB stars through tidal interactions. In this review,
however, I consider a more fundamental role for multiplicity and explore claims
that the Be phenomenon may be intimately linked to binarity. I describe the
binary channel for the formation of Be stars and the ongoing discussion about
the relative contribution of this channel to the population of Be stars. I also
present evidence suggesting that some environments are more favourable for the
appearance of Be stars and explore whether this may be connected to initial
conditions, such as the chemical composition or the distribution of rotational
velocities on the ZAMS.
