EEG research has a rich history of providing biomarkers for behavioral traits and mental health disorders. The primary interest of ENIGMA‐EEG is, however, not to repeat biomarker research in larger samples. Individual variation in many of the EEG biomarkers has been found to be under substantial genetic control, with twin and family studies provided the crucial information that EEG trait variation is heritable. Early studies, dating back to the 1930s, pointed toward nearly identical recordings of resting EEG in identical twins (reviewed in van Beijsterveldt and Boomsma (1994)). The first large‐scale twin studies carried out by Friedrich Vogel (1958); described in Vogel (1970) demonstrated that differences between monozygotic twins did not exceed those seen in successive EEG recordings from the same individual, leading to the conclusion that variability in EEG features is nearly completely determined by a multifactorial genetic system. Subsequent studies of other resting EEG features in children, adolescents, and adults showed that EEG measures of oscillation power, oscillation dynamics, and connectivity are heritable traits (Anokhin et al., 2001; van Beijsterveldt & van Baal, 2002; van Beijsterveldt & van
