  We recall the obstacles which seemed, long ago, to prevent one from viewing
supersymmetry as a possible fundamental symmetry of Nature. Is spontaneous
supersymmetry breaking possible ? Where is the spin-1/2 Goldstone fermion of
supersymmetry, if not a neutrino ? Which bosons and fermions could be related ?
Can one define conserved baryon and lepton numbers in such theories, although
they systematically involve self-conjugate Majorana fermions ? If we have to
postulate the existence of new bosons carrying B and L (the new spin-0 squarks
and sleptons), can we prevent them from mediating new unwanted interactions ?
  We then recall how we obtained the three basic ingredients of the
Supersymmetric Standard Model: 1) the SU(3) x SU(2) x U(1) gauge superfields;
2) the chiral quark and lepton superfields; 3) the two doublet Higgs
superfields responsible for the electroweak breaking, and the generation of
quark and lepton masses. The original continuous ``R-invariance'' of this model
was soon abandoned in favor of its discrete version, R-parity, so that the
gravitino, and gluinos, can acquire masses - gluinos getting their masses from
supergravity, or radiative corrections.
  R-parity forbids unwanted squark and slepton exchanges, and guarantees the
stability of the ``lightest supersymmetric particle''. It is present only since
we restricted the initial superpotential to be an even function of quark and
lepton superfields (so as to allow for B and L conservation laws), as made
apparent by the formula re-expressing R-parity as (-1)^2S (-1)^(3B+L). Whether
it turns out to be absolutely conserved, or not, R-parity plays an essential
role in the phenomenology of supersymmetric theories, and the experimental
searches for the new sparticles.
