Electroencephalography (EEG) as a noninvasive measurement technique is recorded from the scalp. Hence, it does not measure any signal directly at cell level but rather the signal that reaches the electrodes. Therefore, EEG should be considered in the context of human physiology which interacts with and influences the EEG signal. This chapter discusses aspects of macroscopic head anatomy and physiology that affect the EEG signal. The focus will be on ocular, muscular and skin potentials, and vascular activity, and how they influence the EEG signal.