  Recent advances in the QCD corrections to $b\to s\gamma$ decay in the MSSM
include i.) evaluation of the relevant operators, Wilson coefficients and
anomalous dimension matrix elements for the various MSSM effective theories
valid at scales beyond $Q =M_W$, ii.) calculations of most of the needed
anomalous dimension matrix elements to next-to-leading order for scales
$m_b\alt Q <M_W$, and iii.) calculations of ${\cal O}(\alpha_s)$ virtual and
bremsstrahlung corrections to the $b\to s\gamma$ decay operators at scale
$Q\sim m_b$. We assemble all these known results to gain an estimate of $B(b\to
s\gamma )$ for the parameter space of the minimal supergravity model (mSUGRA).
We find a much reduced scale dependence of our result compared to usual
leading-log evaluations. Comparison with the latest CLEO results yields
stringent constraints on parameter space. Much of mSUGRA parameter space is
ruled out for $\mu <0$, especially for large $tan\beta$. We compare these
results with other constraints from cosmology and non-standard vacua. Also, we
compare with expectations for discovering mSUGRA at LEP2, the Tevatron and the
CERN LHC.
