  Here we describe the observations and the resulting constraints on the upper
atmosphere (thermosphere and exosphere) of the "Hot-Jupiters". In particular,
observations and theoretical modeling of Hot-Jupiter evaporation are described.
The observations allowed the discovery that the planet orbiting HD209458 has an
extended atmosphere of escaping hydrogen and showed the presence of oxygen and
carbon at very high altitude. These observations give unique constraints on the
escape rate and mechanism in the atmosphere of these planets. The most recent
Lyman-alpha HST observations of HD189733b allows for the first time to compare
the evaporation from two different planets in different environments. Models to
quantify the escape rate from the measured occultation depths, and an energy
diagram to describe the evaporation state of Hot-Jupiters are presented. Using
this diagram, it is shown that few already known planets could be remnants of
formerly giant planets.
