  Since planets were first discovered outside our own Solar System in 1992
(around a pulsar) and in 1995 (around a main sequence star), extrasolar planet
studies have become one of the most dynamic research fields in astronomy. Now
that more than 370 exoplanets have been discovered, focus has moved from
finding planets to characterise these alien worlds. As well as detecting the
atmospheres of these exoplanets, part of the characterisation process
undoubtedly involves the search for extrasolar moons. A review on the current
situation of exoplanet characterization is presented in Chapter 3. We focus on
the characterization of transiting planets orbiting very close to their parent
star since for them we can already probe their atmospheric constituents. By
contrast, the second part of the Chapter is dedicated to the search for
extraterrestrial life, both within and beyond the Solar System. The
characteristics of the Habitable Zone and the markers for the presence of life
(biosignatures) are detailed. In Chapter 4 we describe the primary transit
observations of the hot Jupiter HD 209458b we obtained at 3.6, 4.5, 5.8 and 8.0
micron using IRAC/Spitzer. Chapter 5 is dedicated to the search for exomoons,
we review a model for the TTV and TDV signals which permits not only the
identification of exomoons but also the derivation of some of their
characteristics. Finally, in Chapter 6 the detectability of a habitable-zone
exomoon around various configurations of exoplanetary systems with the Kepler
Mission or photometry of approximately equal quality is investigated. We find
that habitable-zone exomoons down to 0.2 Earth Masses may be detected.
