Behavioral extremism takes different forms and shapes, including violent extremism, extreme dieting, extreme passion, and extreme infatuations. The authors look at these various behaviors through the lens of the goal systems theory and argue that all cases of extremism stem from motivational imbalance whereby a given need (or a goal serving this need) gains dominance and overrides other basic concerns. The result is an expansion of behavioral options for addressing the prioritized need and engagement in extreme behaviors forbidden under the state of balance. Further, the authors discuss the antecedents of motivational imbalance with a particular focus on individual differences. They argue that some people personify the dynamics of extremism more than others and propose a construct of "extreme personality" to reflect between-person variation in proneness to motivational imbalance. They cite evidence showing that extreme personality predicts manifestations of extremism at different levels: motivational, cognitive, affective, behavioral, and social. They conclude by discussing future research directions.