This study examines the alternative ways that key personality traits—Agreeableness and Conscientiousness—work in conjunction with measures of situational opportunity in affecting offending and victimization simultaneously. More specifically, we explore (a) the extent to which the effects of Agreeableness and Conscientiousness on offending and victimization are mediated by opportunity, and (b) the extent to which the effects of Agreeableness and Conscientiousness on offending and victimization are moderated by opportunity. These interrelationships are estimated using path modeling of two waves of survey data from a 4-year panel study of 2,220 adolescents. Results suggest that the effects of Agreeableness and Conscientiousness on offending and/or victimization are partially mediated by situational opportunity. Regarding interaction effects, results show that the effects of Agreeableness and Conscientiousness are also moderated by measures of situational opportunity. These traits appear to protect against offending most notably at the highest levels of opportunity.