  The last few years has seen a dramatic increase in the number of exoplanets
known and in the range of methods for characterising their atmospheric
properties. At the same time, new discoveries of increasingly cooler brown
dwarfs have pushed down their temperature range which now extends down to
Y-dwarfs of <300 K. Modelling of these atmospheres has required the development
of new techniques to deal with the molecular chemistry and clouds in these
objects. The atmospheres of brown dwarfs are relatively well understood, but
some problems remain, in particular the behavior of clouds at the L/T
transition. Observational data for exoplanet atmosphere characterization is
largely limited to giant exoplanets that are hot because they are near to their
star (hot Jupiters) or because they are young and still cooling. For these
planets there is good evidence for the presence of CO and H2O absorptions in
the IR. Sodium absorption is observed in a number of objects. Reflected light
measurements show that some giant exoplanets are very dark, indicating a cloud
free atmosphere. However, there is also good evidence for clouds and haze in
some other planets. It is also well established that some highly irradiated
planets have inflated radii, though the mechanism for this inflation is not yet
clear. Some other issues in the composition and structure of giant exoplanet
atmospheres such as the occurence of inverted temperature structures, the
presence or absence of CO2 and CH4, and the occurrence of high C/O ratios are
still the subject of investigation and debate.
