We present a bottom-up approach to the question of supersymmetry break
ing in the MSSM. Starting with the experimentally measurable low-energ
y supersymmetry-breaking parameters, which can take any values consist
ent with present experimental constraints, we evolve them up to an arb
itrary high energy scale. Approximate analytical expressions for such
an evolution, valid for low and moderate values of tan beta, are prese
nted. We then discuss qualitative properties of the high-energy parame
ter space and, in particular, identify the conditions on the low-energ
y spectrum that are necessary for the parameters at the high-energy sc
ale to satisfy simple regular pattern such as universality or partial
universality. As an illustrative example, we take low-energy parameter
s for which light sparticles, within the reach of the LEP2 collider, a
ppear in the spectrum, and which do not affect the Standard Model agre
ement with the precision measurement data. Comparison between supersym
metry breaking at the GUT scale and at a low-energy scale is made. (C)
1997 Elsevier Science B.V.