This chapter explores the impact of anesthesia on the brain’s bioelectrical activity, emphasizing the clinical and research implications for anesthetic depth monitoring and surgical safety. Spontaneous brain electrical activity, as recorded by electroencephalography (EEG), and evoked potentials form the basis for understanding cortical function under anesthesia. EEG waveforms (alpha, beta, theta, delta, and gamma) vary with states of consciousness and provide real-time insights into anesthesia depth through indices like the bispectral index (BIS) and Narcotrend. The chapter also delves into cortical evoked potentials, including somatosensory, auditory, and visual evoked potentials, highlighting their utility in assessing neural pathway integrity and guiding surgical procedures. Advances in signal processing and machine learning are expanding the diagnostic and therapeutic potential of brain electrical monitoring in anesthesia.