Both aggression and deliberate emotion regulation have been the focus of considerable scholarly attention. However, little research has examined the contribution of maladaptive emotion regulation to aggressive behaviour, beyond that of under-controlled anger. Given the high cost of aggressive behaviour to public health and justice systems across the world, identifying and addressing factors that contribute to aggression, including emotion regulation, is an important priority. Against this background, the three broad aims of this thesis were to a) establish whether maladaptive emotion regulation is associated with higher levels of aggression in offending adults; b) determine whether a key aspect of maladaptive emotion regulation – difficulty attending to upsetting emotions – is associated with higher levels of aggression in offending adults, even after controlling for trait anger and anger control; and c) determine whether three emotion skills – emotional awareness, emotional acceptance, and access to a variety of emotion regulation strategies – are associated with adaptive emotion regulation in offending adults. After reviewing and integrating relevant literature from the field of emotion regulation with a contemporary model of aggression, two empirical studies were conducted. A preliminary study was undertaken to ascertain whether a written measure of emotional awareness, proposed for inclusion in the main study and requiring a high level of literacy, was suitable to be administered orally. Oral administration of this measure was considered necessary given that offenders have generally been shown to have poor literacy. The results of this study, undertaken with undergraduate psychology students and community members, showed that the measure was suitable for oral administration. It was therefore included in the main study. Following this, the main study was undertaken using offenders recruited from Community Corrections Offices across Melbourne, Australia, to determine whether a maladaptive style of emotion regulation was associated with a history of aggressive behaviour. Participants completed self-report measures relating to history of aggression, difficulties in emotion regulation, emotional awareness, normative beliefs supportive of aggression, anger experience and control, and verbal intelligence. Participants also completed a performance-based measure of emotional awareness. Results of the main study revealed that offenders with a maladaptive emotion regulation style reported more extensive histories of aggression than those with an adaptive emotion regulation style. Results also indicated that offenders reporting difficulty attending to their emotions had more extensive histories of aggression than those who did not report such difficulties, even after controlling for trait anger and ability to control the outward expression of anger. Finally, self-reported emotional awareness and access to effective emotion regulation strategies were found to relate to adaptive emotion regulation. Several important clinical implications arise from the results of this research. The finding that maladaptive emotion regulation is associated with a more extensive history of aggression suggests that intervention directed at enhancing adaptive emotion regulation may prove a useful addition to existing aggression and violent offending treatment programs. Further, the association that self-reported emotional awareness and access to effective emotion regulation strategies were found to have with adaptive emotion regulation suggests that these areas will form useful treatment targets. Finally, the finding that difficulty attending to emotions is associated with a more extensive history of aggression also speaks to the importance of ensuring that current programs and treatments seek to assist participants to control problem behaviour associated with emotional arousal, rather than to control their emotions (particularly anger) per se.