  The Next-Generation Very Large Array (ngVLA) has the potential to be a
workhorse for the discovery and study of paired supermassive black holes either
at large separations (dual) or in tightly bound systems (binary). In this
chapter, we outline the science case for the study of these supermassive pairs,
and summarize discovery methods that can be used at radio wavelengths to
discover them: including morphological, spectral, and time-domain
identifications. One critical aspect of this work is that multi-messenger
binary black hole studies may be possible with the ngVLA when combined with
gravitational-wave searches using pulsar timing array techniques. However,
long-baseline interferometery (>>1000 km) will make this possibility more
likely by expanding the redshift range at which radio emission arising from two
separate black holes may be resolved and studied.
