  The status of the Standard Model (SM) is reviewed. We emphazize the fact that
in spite of the success of the SM for the descrition of the fermionic sector,
the status of the bosonic sector (gauge and scalar) suffers from many
theoretical deficiencies and from the lack of empirical support. This
situation, which leaves room for several types of extensions or alternatives to
SM, strongly motivates the pursue of intense efforts for finding hints of New
Physics (NP) effects. We present a phenomenological description valid for
energies lying below the NP scale. We discuss the indirect constraints
established from high precision tests at LEP1, as well as the direct tests that
could be performed at future machines
