Some possible approaches to the dark energy in string theory are
presented. I will mainly focus on models in which potentials for the
dark energy are essentially derived by classical objects. The minimal
ingredients for the cosmological constant are specified potentially in
IIA/IIB. On the other hand, the time-varying dark energy can be
realized by an axion with weakly broken shift-symmetry, even in the
presence of high-scale moduli stabilization and SUSY breaking.