This PhD aimed to understand the constructs of aggression motivation and inhibition among prisoners. The research explored the role of developmental, affect, personality and socio-cognitive factors in aggression, investigating how these factors contributed to motives and inhibitors. This addressed several gaps in our knowledge and understanding of these factors among prisoners. In doing so, it contributed to the proposal of an empirically informed developmental model of aggression motivation and inhibition for prisoners, a model potentially capable of accounting for the theoretical and clinical limitations of existing explanatory models. Study one involved 206 adult men from a medium secure prison. This study specifically examined the role of aggression (using the Aggression Motivation Questionnaire, AMQ; Ireland, 2007) and offence motivation (with the Offence Motivation Questionnaire, OMQ; Gudjonsson & Sigurdsson, 2004) and affect (using the Multidimensional Anger Inventory, MAI; Sigel, 1989). Contrary to predictions, aggression motivation extended beyond the traditional reactive versus proactive distinction, with four core motivations identified. Further challenging the previous dichotomous distinction were findings that affect was related to all motivations and not just reactive aggression. The structure of offence motivation was consistent with previous research suggesting the validity of such motivation. Relationships found between individual offence and aggression motives supported longstanding notions in the human motivation and rationale choice literature that a limited number of motivations are capable of accounting for the diversity of human behaviour. Study one strengthens the argument to further examine and understand the factors contributing to such aggression motivations, such as cognition or developmental and life course experiences. Study two recruited 210 adult male prisoners to examine the developmental and socio-cognitive factors underpinning aggression motivations. Confirmation as to the structure of aggression motivation was also evaluated. It was predicted that differing developmental and socio-cognitive factors would relate to each motivation. Analysis supported this and thus further understanding was achieved as to the contribution of these factors. Reformulation of existing developmental models of aggression and the importance of social cognition for adult prisoners were consequently highlighted. However, attempts to confirm the four-factor solution for aggression motivation identified in Study 1 was not achieved. Exploratory factor analysis supported the extraction of a three-component solution from the AMQ, which was underpinned by ‘protection’, ‘pleasure’ and ‘positive outcomes’ motivations. This raised doubt as to the underlying structure of aggression motivation, which required further examination. Study three involved 234 prisoners from two separate prisons. All participants were adult men. This study facilitated the further exploration of maladaptive personality and affect regulation strategies in aggression motivation. Evaluation of the components of aggression inhibition was also undertaken. As expected, personality and affect regulation strategies were individually associated with aggression motives and inhibitors. This suggested that these factors had a unique contribution to aggression motivations and inhibitors. A four component structure for aggression inhibition was identified through exploratory factor analysis. The three factor structure for aggression motivation indicated by Study 2 was supported by confirmatory factor analysis. The findings gained from this study were combined with previous studies and influenced the development of the Applied Integrated Model of Aggression Motivation (AIM-AM). This new proposed integrated model of aggression is described in detail in the last Chapter of this thesis. The current research highlights the importance of considering aggression motivation and inhibition by demonstrating how valuable information to assist our understanding of aggression can be enhanced through their detailed examination. This research points towards a range of underlying factors which motivate and inhibit aggression in prisoners, including personality traits, developmental and life experiences, cognition and affect regulation. This was drawn together in the AIM-AM, which remains the first proposed aggression model developed specifically from the study of forensic populations. This applied theoretical model and underpinning research has a range of research and clinical implications for those working with prisoners, such as guiding the psychological assessment and risk evaluations of prisoners and focusing interventions to reduce their likelihood of aggression.