  With over 1800 planets discovered outside of the Solar System in the past two
decades, the field of exoplanetology has broadened our perspective on planetary
systems. Research priorities are now moving from planet detection to planet
characterization. In this context, transiting exoplanets are of special
interest due to the wealth of data made available by their orbital
configuration. Here, I introduce two methods to gain new insights into the
atmospheric and interior properties of exoplanets.
  The first method aims to map an exoplanet's atmosphere based on the scanning
obtained while it is occulted by its host star. I introduce the basics of
eclipse mapping, its caveats, and a framework to mitigate their effects via
global analyses including transits, phase curves, and radial velocity
measurements. I use this method to create the first 2D map and the first cloud
map of an exoplanet for the hot-Jupiters HD189733b and Kepler-7b, respectively.
Ultimately temperature, composition, and circulation patterns could be
constrained in 3D, a significant asset for informing atmospheric models.
  The second method, MassSpec, aims to determine transiting planet masses and
atmospheric properties solely from transmission spectra. Determination of an
exoplanet's mass is key to understanding its basic properties, including its
potential for supporting life. To date, mass constraints for exoplanets are
mainly based on radial velocity measurements, which are not suited for planets
with low masses, large semi-major axes, or those orbiting faint or active
stars. I demonstrate that a planet's mass has to be accounted for by
atmospheric retrieval methods to avoid biases and that JWST could determine the
mass and atmospheric properties of half a dozen Earth-sized planets in their
host's habitable zones over its lifetime, which could lead to the first
identification of a habitable exoplanet.
