In this paper we compute one-loop corrections to masses and couplings
in the minimal supersymmetric standard model. We present explicit
formulae for the complete corrections and a set of compact
approximations which hold over the unified parameter space associated
with radiative electroweak symmetry breaking. We illustrate the
importance of the corrections and the accuracy of our approximations
by scanning over the parameter space. We calculate the supersymmetric
one-loop corrections to the $W$-boson mass, the effective weak mixing
angle, and the quark and lepton masses, and discuss implications for
gauge and Yukawa coupling unification. We also compute the one-loop
corrections to the entire superpartner and Higgs-boson mass spectrum.
We find significant corrections over much of the parameter space, and
illustrate that our approximations are good to ${\cal O}(1\%)$ for
many of the superparticle masses.