Renormalization of Supersymmetric Theories

We review the renormalization of the electroweak sector of the standard model. The derivation also applies to the minimal supersymmetric standard model. We discuss regularization and the relation between the threshold corrections and the renormalization group equations. We consider the corrections to many precision observables, including MW and sin^2 theta^eff. We show that global fits to the data exclude regions of supersymmetric model parameter space and lead to lower bounds on superpartner masses.