We investigate compactifications of M-theory from 11 → 5 → 4 dimensions and discuss the geometrical properties of 4D moduli fields related to the structure of 5D theory.We study supersymmetry breaking by compactification of the fifth dimension and find that a universal superpotential is generated for the axion-dilaton superfield S. The resulting theory has a vacuum with S = 1, zero cosmological constant and a gravitino mass depending on the fifth radius as m 3 2 R - 2 5 /M P l .We discuss the phenomenological aspects of this scenario, mainly string unification and the decompactification problem.