String Theory in particular
(here an old review paper, and a recent lecture)
and quantum field theory in general,
especially non-perturbative aspects of supersymmetric theories and duality.
Currently my interests are in the quantum geometry of D-branes, in particular
in the interplay between open topological strings,
homological mirror symmetry and the Landau-Ginzburg realization of the category of topological branes.
After having served as head of the Theory Group at CERN, my current main duties at CERN include being
chairman of the Fellows and Associates Committee of TH, and organizer of the CERN general colloquium.
I am also honorary professor at the Dept for Physics and Astronomy of the University of Heidelberg.