The moduli of N=1 compactifications of IIB string theory can be stabilized by
a combination of fluxes (which freeze complex structure moduli and the dilaton)
and nonperturbative superpotentials (which freeze Kahler moduli), typically
leading to supersymmetric AdS vacua. We show that stringy corrections to the
Kahler potential qualitatively alter the structure of the effective scalar
potential even at large volume, and can give rise to non-supersymmetric vacua
including metastable de Sitter spacetimes. Our results suggest an approach to
solving the cosmological constant problem, so that the scale of the 1-loop
corrected cosmological constant can be much smaller than the scale of
supersymmetry breaking.
