  The connection between the standard $H^\infty$-problem in control theory and
Nevanlinna-Pick interpolation in operator theory was established in the 1980s,
and has led to a fruitful cross-pollination between the two fields since. In
the meantime, research in $H^\infty$-control theory has moved on to the study
of robust control for systems with structured uncertainties and to various
types of multidimensional systems, while Nevanlinna-Pick interpolation theory
has moved on independently to a variety of multivariable settings. Here we
review these developments and indicate the precise connections which survive in
the more general multidimensional/multivariable incarnations of the two
theories.
