  The demographic of circumstellar disks, the birthplaces of planets, is
diverse and rich in disks featuring rings, gaps, spirals, filaments, and arcs.
Many studies revealing these disk structures have focused on objects around
single stars and disks in isolation. The scenario is more complex if binarity
or multiplicity is involved; most stars are part of multiple systems in crowded
star-forming regions. How does the presence of one or more stellar companions
affect the shape and size of the circumstellar disks? Here we review the
landscape of results from optical, infrared, and (sub-) millimeter observations
of the effects of multiplicity on protoplanetary disks, emphasizing the
demographic studies of nearby molecular clouds and the high-resolution studies
of multiple disk systems.
