  Ground-based and spacecraft telescopic observations, combined with an
intensive modeling effort, have greatly enhanced our understanding of hot giant
planets and brown dwarfs over the past ten years. Although these objects are
all fluid, hydrogen worlds with stratified atmospheres overlying convective
interiors, they exhibit an impressive diversity of atmospheric behavior. Hot
Jupiters are strongly irradiated, and a wealth of observations constrain the
day-night temperature differences, circulation, and cloudiness. The intense
stellar irradiation, presumed tidal locking and modest rotation leads to a
novel regime of strong day-night radiative forcing. Circulation models predict
large day-night temperature differences, global-scale eddies, patchy clouds,
and, in most cases, a fast eastward jet at the equator-equatorial
superrotation. The warm Jupiters may exhibit a wide range of rotation rates,
obliquities, and orbital eccentricities, which, along with the weaker
irradiation, leads to circulation patterns and observable signatures predicted
to differ substantially from hot Jupiters. Brown dwarfs are typically isolated,
rapidly rotating worlds; they radiate enormous energy fluxes into space and
convect vigorously in their interiors. Their atmospheres exhibit patchiness in
clouds and temperature on regional to global scales-the result of modulation by
large-scale atmospheric circulation. Despite the lack of irradiation, such
circulations can be driven by interaction of the interior convection with the
overlying atmosphere, as well as self-organization of patchiness due to
cloud-dynamical-radiative feedbacks. Finally, irradiated brown dwarfs help to
bridge the gap between these classes of objects, experiencing intense external
irradiation as well as vigorous interior convection. A hierarchy of modeling
approaches have yielded major new insights into the dynamics governing these
phenomena.
