  Rapporteur talk at the International Europhysics Conference on High Energy
Physics, Brussels (Belgium), July 27-August 2, 1995. This talk begins with a
brief general introduction to the extensions of the Standard Model, reviewing
the ideology of effective field theories and its practical implications. The
central part deals with candidate extensions near the Fermi scale, focusing on
some phenomenological aspects of the Minimal Supersymmetric Standard Model. The
final part discusses some possible low-energy implications of further
extensions near the Planck scale, namely superstring theories.
