Three hypotheses concerning the association between instrumental (I) and expressive (E) beliefs about aggression and physical aggression were assessed among a sample comprising students (n ¼ 40), women from a domestic violence shelter (n ¼ 29), and male prisoners (n ¼ 46), all of whom had committed at least one act of physical aggression to a partner. Participants completed an adapted version of the EXPAGG [Archer and Haigh (1997a): British Journal of Social Psychology 35:1-23] to measure I and E beliefs about aggression, the Conflict Tactics Scale (CTS) [Straus (1979): Journal of Marriage and the Family 41:75-88] for themselves and their partner, and measures of fear and injuries resulting from partner violence. I beliefs predicted self-reported physical aggression to the partner, most CTS acts of physical aggression, and injuries to the partner, with only minor and limited associations for E beliefs. Correlations for the student and prisoner samples, and for men and women, showed different strengths. The findings supported a general link between I beliefs and aggression but offered no support for the predictions that the link would be restricted to men or to men who showed a persistent pattern of violence to their partners. Aggr. Behav. 29:41-54,