As optical lithography continues to extend into low-k1 regime, resolution of mask patterns continues to diminish. The limitation of 1.35 NA posed by water-based lithography has led to the application of various resolution enhancement techniques (RET), for example, use of strong phase-shifting masks, aggressive OPC and sub-resolution assist features, customized illuminators, etc. The adoption of these RET techniques combined with the requirements to detect even smaller defects on masks due to increasing MEEF, poses considerable challenges for a mask inspection engineer. Inspecting masks under their actinic-aerial image conditions would detect defects that are more likely to print under those exposure conditions. However, this also makes reviewing such defects in their low-contrast aerial images very challenging. On the other hand, inspecting masks under higher resolution or mask-plane inspection optics would allow for better viewing of defects post-inspection. However, such inspections generally would also detect many more defects, including critical and nuisance, thereby making it difficult to judge which are of real concern for printability on wafer. Hence, a comprehensive approach is needed in handling defects both post-aerial and post-high resolution inspections. This paper focuses on review of defects post high resolution or mask-plane inspections, especially in the wafer-fab environment. A later paper will focus on review of defects post aerial-image inspections.