This study examines the relative importance of individual differences in relation to perceptions of work–family conflict and facilitation, as well as the moderating role of boundary preference for segmentation on these relationships. Relative importance analyses, based on a diverse sample of 380 employees from the USA, revealed that individual differences were consistently predictive of self-reported work–family conflict and facilitation. Conscientiousness, neuroticism, negative affect and core self-evaluations were consistently related to both directions of work–family conflict, whereas agreeableness predicted significant variance in family-to-work conflict only. Positive affect and core self-evaluations were consistently related to both directions of work–family facilitation, whereas agreeableness and neuroticism predicted significant variance in family-to-work facilitation only. Collectively, individual differences explained 25–28% of the variance in work–family conflict (primarily predicted by neuroticism and negative affect) and 11–18% of the variance in work–family facilitation (primarily predicted by positive affect and core self-evaluations). Moderated regression analyses showed that boundary preference for segmentation strengthened many of the relationships between individual differences and work–family conflict and facilitation. Implications for addressing the nature of work and family are discussed. Copyright © 2012 John Wiley & Sons, Ltd.