  Embedding hidden sector supergravity models in the framework of string theory
leads to the appearance of axion-like degrees of freedom. Among them is the
model independent axion of heterotic string theory. It has a decay constant of
order of the Planck scale and could play the role of a quintessence field. In
models allowing for the required $\mu$ term in the TeV range, the hidden sector
dynamics leads to a vacuum energy of $(0.003 {\rm eV})^4$ via a multiple
see-saw effect. A solution to the strong CP-problem is provided by an
additional hidden sector pseudoscalar with properties that make it an
acceptable candidate for cold dark matter of the universe.
