  We construct a four dimensional chiral N=1 space-time supersymmetric Type I
vacuum corresponding to a compactification on a toroidal Z_2 X Z_2 X Z_3
orbifold. Using recent results in four dimensional orientifolds, we argue that
this model has a well defined world-sheet description. An interesting feature
of this model is that the gauge group contains an SU(6) subgroup with three
chiral generations. Moreover, this model contains D5-branes and therefore
corresponds to a non-perturbative heterotic vacuum. This is the first example
of a consistent chiral N=1 supersymmetric string vacuum which is
non-perturbative from the heterotic viewpoint, has a perturbative description
in a dual theory, and possesses some phenomenologically interesting
characteristics. We also compute the tree-level superpotential in this theory
