Statement of problem: Although Zirconia based all ceramic restorations are widely used, the marginal accuracy of these restorations has been a controversy. Purpose: The purpose of this study was to assess the effect of different veneering techniques, different framework margin designs, and two finish line thicknesses on the marginal accuracy of zirconia based all ceramic crowns. Material and methods: Thirty zirconia-based crowns were fabricated using CEREC CAD/CAM system on specially designed stainless steel dies. The crowns were divided into three groups of ten crowns each: Group 1: received CAD/CAM fabricated glass ceramic veneer caps, Group 2: received Press-over glass ceramic veneer caps and Group 3: received Conventional layered glass ceramic veneer caps. Each group of Ten crowns was subdivided into two subgroups of five crowns each: Subgroup 1: 0.9 mm shoulder with rounded internal angle finish line and Subgroup 2: 1.2 mm shoulder with rounded internal angle finish line. The vertical marginal fit of all tested crowns was evaluated using a stereomicroscope. Finally, all the data and results were collected, tabulated and statistically analyzed. Results: The results showed that the veneering technique, the finish line thickness and the interaction between them had no significant effect on the marginal gap. There was significant difference between 1.2 mm press-over and 1.2 mm layering technique groups. Conclusions: Different veneering techniques together with different core margin designs can be safely used. However, in 1.2 mm finish line thickness, the layering technique is the least recommended.