D-brane instantons on the T6/Z3 orientifold

We give a detailed microscopic derivation of gauge and stringy instanton gen erated superpotentials for gauge theories living on D3-branes at Z(3)-orientifold singularities. Gauge instantons are generated by D(-1)-branes and lead to Affleck, Dine and Seiberg (ADS) like superpotentials in the effective N = 1 gauge theories with three generations of bifundamental and anti/symmetricmatter.Stringy instanton effects are generated by Euclidean ED3-branes wrapping four cycles onT(6)/Z(3).They give rise to Majorana masses,Yukawa couplings or non-renormalizable superpotentials depending on the gauge theory.Finally we determine the conditions under which ADS like superpotentials are generated in N = 1gauge theories with adjoints, fundamentals, symmetric and antisymmetric chiral matter.