The common Passive Voltage Contrast (VC) localization method is based on brightness differences of conducting structures in SEM and FIB images and can be used for failure localization issues. The Active Voltage Contrast method (AVC) offers even more localization possibilities. Particularly the PVC methods became widely accepted in the semiconductor FA community. Nearly all labs make use of it. There are several Voltage Contrast mechanisms in SEM and FIB and not all of them are always completely understood. This tutorial will give a comprehensive overview over all phenomena related to this subject. The multiple advantages, possibilities and limits of VC failure localization are systematized and discussed.