  The formation of massive stars in close binary systems is complicated due to
their high radiation pressure, the crowded environment and the expected minimum
separation for fragmentation being many times greater than the orbital
separation. I discuss how massive star formation can be understood as being due
to competitive accretion in stellar clusters. Massive binary systems are then
formed due to accretion onto wider low-mass systems. The combination of
accretion and dynamical interactions with other stars in the cluster then
result in producing a close binary system. Tidal and 3-body captures in dense
stellar cores can also play a role in forming massive binary systems while
stellar mergers of such close binary systems due to interactions may play an
important role in overcoming the radiation pressure.
