  The structure of stringy quantum corrections to four-dimensional effective
theories is particularly interesting for string phenomenology and attempts to
stabilize moduli. We consider the heterotic string compactified on a Calabi-Yau
space. For this case, we compute the leading corrections to the kinetic terms
of moduli fields. The structure of these corrections is largely dictated by the
underlying higher-dimensional extended supersymmetry. We find corrections
generically of order (alpha')^2 rather than of order (alpha')^3 found in type
II compactifications or heterotic compactifications with the standard
embedding. We explore the implications of these corrections for breaking
no-scale structure.
