Supersymmetric loop effects

We review the loop effects of the low energy supersymmetry. The global success of the Standard Model rises two related questions: how strongly the mass scales of the superpartners are constrained and can they be, nevertheless, indirectly seen in precision measurements. The bulk of the electroweak data is well screened from supersymmetric loop effects, due to the structure of the theory, even with superpartners generically light, $O(M_Z)$. The only exception are the left-handed squarks of the third generation which have to be $\simgt O(300$ GeV) to maintain the success of the SM. The other superpartners can still be light, at their present experimental mass limits, and would manifest themselves through virtual corrections to the small number of observables such as $R_b, b \to s\gamma, K^0-\bar K^0$ and $B^0-\bar B^0$ mixing and a few more for large $tan\beta$. Those effects require still higher experimental precision to be detectable.