The study of habitability is certainly an interdisciplinary venture including astrophysical, biological geophysical and chemical studies. In this session we will analyze the astrophysical point of view. The so-called habitable zone (HZ) of a planetary system is defined as the region around a star where liquid water is stable on the surface of an Earth-like planet. Therefore, we will discuss the following basic requirements for habitability:
(i) the stellar influence on the distance of the HZ,
(ii) the mass, the composition and the atmosphere of a possible habitable planet and
(iii) the long-term stability of planetary systems.
Furthermore, contributions about the detection of Earth-size planets -- including observations of CoRoT and Kepler as well as ground-based observations and futur missions like GAIA -- will be of great interest, to show what might be possible in this field of research in the next future.