  This article gives an overview of recent theoretical and experimental
findings concerning the hydrodynamic interaction between liquid-embedded
particles in various confined geometries. A simple unifying description
emerges, which accounts for the various findings based on the effect of
confinement on conserved fields of the embedding liquid. It shows, in
particular, that the hydrodynamic interaction under confinement remains
long-ranged, decaying algebraically with inter-particle distance, except for
the case of confinement in a rigid linear channel.
