Gray (1987) proposed two systems that underlie much of our behaviour and personality. One system relates to avoidance or withdrawal behaviour, called the Behavioural Inhibition System (BIS), whereas the other system relates to approach behaviour, called the Behavioural Approach System (BAS). In two samples, it was investigated whether individual differences in surface of personality as described by the Big Five can be explained by BIS/BAS. Neuroticism and Extraversion could be explained well by BIS/BAS, but also for Agreeableness and Conscientiousness consistent findings were obtained. Copyright © 2006 John Wiley & Sons, Ltd.