The aim of this TH-institute will be to discuss recent developments in theoretical aspects of black holes, in particular on understanding the fate of the classical horizon at the quantum level. In classical General Relativity, black holes are the generic endpoint of gravitational collapse. They are characterized by an event horizon separating two causally disconnected regions, one visible to an asymptotic observer, the other accessible to an infalling observer. Semi-classical reasoning suggests that black holes decay by Hawking emission and eventually disappear. This is in potential conflict with the basic postulates of quantum mechanics, which require that information carried by the collapsing matter must be conserved. This paradox has catalyzed most of the recent progress in understanding the nature of quantum gravity, but has eluded a fully satisfactory solution so far. Recent thoughts experiments suggest that the semi-classical picture of a smooth, eventless horizon may be invalid, at least for old black holes which have radiated most of their entropy. The alternative to this semi-classical picture has been widely discussed over the last year, with no definite answer yet. The workshop will focus on the implications of these thought experiments for the fundamental nature of gravity, and related issues. The workshop will bring together leading quantum gravity experts to discuss these issues, with a light schedule of seminars leaving plenty of time for informal discussions.