During the last decennium, a growing number of depth of anesthesia monitors, extracting information from the spontaneous electroencephalogram (EEG) have been developed and commercialized. The growing interest in depth of anesthesia monitoring resulted in an intensified technological progress. Innovations on both hardware and mathematical algorithms were introduced for improving the extraction of data. Because of the abundance of monitors now commercially available, it becomes increasingly important to develop a standardized reproducible methodology for comparing depth of anesthesia monitors. In this review, the authors present a strategy to compare monitors of the hypnotic component of anesthesia, based on the available literature and their own experience with validation studies. They also discuss the level of validation of the most commonly used EEG derived depth of anesthesia monitors.