  The study of exoplanetary atmospheres is one of the most exciting and dynamic
frontiers in astronomy. Over the past two decades ongoing surveys have revealed
an astonishing diversity in the planetary masses, radii, temperatures, orbital
parameters, and host stellar properties of exoplanetary systems. We are now
moving into an era where we can begin to address fundamental questions
concerning the diversity of exoplanetary compositions, atmospheric and interior
processes, and formation histories, just as have been pursued for solar system
planets over the past century. Exoplanetary atmospheres provide a direct means
to address these questions via their observable spectral signatures. In the
last decade, and particularly in the last five years, tremendous progress has
been made in detecting atmospheric signatures of exoplanets through photometric
and spectroscopic methods using a variety of space-borne and/or ground-based
observational facilities. These observations are beginning to provide important
constraints on a wide gamut of atmospheric properties, including
pressure-temperature profiles, chemical compositions, energy circulation,
presence of clouds, and non-equilibrium processes. The latest studies are also
beginning to connect the inferred chemical compositions to exoplanetary
formation conditions. In the present chapter, we review the most recent
developments in the area of exoplanetary atmospheres. Our review covers
advances in both observations and theory of exoplanetary atmospheres, and spans
a broad range of exoplanet types (gas giants, ice giants, and super-Earths) and
detection methods (transiting planets, direct imaging, and radial velocity). We
close with a discussion of the bright prospects for future studies of
exoplanetary atmospheres.
