  Recent advances in the calculation of the $b\to s\gamma$ decay branching
ratio are presented in the context of supersymmetric theories. Theoretical
accuracy increased by inclusion of the next-to-leading order QCD corrections
makes it possible to significantly decrease scale dependence of the result.
Comparison with the latest CLEO experimental results then allows to limit
supersymmetric loop contributions to the process and consequently constrain the
parameter space of supersymmetric extensions of the Standard Model. We discuss
these constraints both in the minimal supergravity inspired model (SUGRA) and
in the simplest gauge-mediated supersymmetry breaking model (GMSB) both of
which are interesting from the point of view of the searches for supersymmetry
at present and future colliders. Our analysis also includes the interesting
region of large $\tan \beta$ relevant for models with Yukawa coupling
unification.
