Statement of problem: Although Zirconia based all ceramic restorations are now widely used, high failure rates due to post chipping of the veneering porcelain has been identified as a major technical complication. Purpose: The purpose of this study was to evaluate the fracture resistance of CAD/CAM zirconia crowns veneered with different techniques: CAD veneering technique with glass joining, CAD veneering technique with adhesive resin bonding and Conventional layering technique. Material and Methods: Thirty zirconia-based crowns were fabricated using CEREC CAD/CAM system on specially designed stainless steel dies. The crowns were divided in to 3 groups according to veneering technique: Group A: CAD/CAM generated zirconia copings received CAD/CAM fabricated high strength veneering caps joined with an intermediate glass joint. (n=10), Group B: CAD/CAM generated zirconia copings received a CAD/CAM fabricated veneering caps joined by adhesive resin cement. (n=10) and Group C: (Control) CAD/CAM generated zirconia copings received conventional veneering by layering technique. (n=10). Each Group of Ten crowns was further subdivided into two subgroups according to treatment: Subgroup 1: (control) Samples not subjected to thermocycling. (n=5), Subgroup 2: Samples subjected to thermocycling. (n=5). Results: The results showed that the veneering technique, thermocycling and the interaction between the two variables had a statistically significant effect on mean failure load. Conclusions: CAD/CAM veneering technique of zirconia cores is a promising way to reduce failures originating from veneering material imperfections and human variables occurring with conventional layering technique.