  In this short review, we summarize our present understanding (and
non-understanding) of exoplanet formation, structure and evolution, in the
light of the most recent discoveries. Recent observations of transiting massive
brown dwarfs seem to remarkably confirm the predicted theoretical mass-radius
relationship in this domain. This mass-radius relationship provides, in some
cases, a powerful diagnostic to distinguish planets from brown dwarfs of same
mass, as for instance for Hat-P-20b. If confirmed, this latter observation
shows that planet formation takes place up to at least 8 Jupiter masses.
Conversely, observations of brown dwarfs down to a few Jupiter masses in young,
low-extinction clusters strongly suggest an overlapping mass domain between
(massive) planets and (low-mass) brown dwarfs, i.e. no mass edge between these
two distinct (in terms of formation mechanism) populations. At last, the large
fraction of heavy material inferred for many of the transiting planets confirms
the core-accretion scenario as been the dominant one for planet formation.
