A Classification of Toroidal Orientifold Models

We develop the general tools for model building with orientifolds, including SS supersymmetry breaking. In this paper, we work out the general formulae of the tadpole conditions for a class of non supersymmetric orientifold models of type IIB string theory compactified on $T^6$, based on the general properties of the orientifold group elements. By solving the tadpoles we obtain the general anomaly free massless spectrum.