  The connection between Supergravity and the low-energy world is analyzed. In
particular, the soft Supersymmetry-breaking terms arising in Supergravity, the
$\mu$ problem and various solutions proposed to solve it are reviewed. The soft
terms arising in Supergravity theories coming from Superstring theory are also
computed and the solutions proposed to solve the $\mu$ problem, which are
naturally present in Superstrings, are also discussed. The $B$ soft terms
associated are given for the different solutions. Finally, the low-energy
Supersymmetric-spectra, which are very characteristic, are obtained.
