Criminology is a multidisciplinary science, and as criminologists, we take pride in that despite the complexities it might cause in the field. I make use of that multidisciplinarity in this dissertation by bringing together the knowledge from neuroscience, evolutionary biology, and behavioural economics to shed light on one of the most unlikely explanatory mechanisms of crime: cooperation. Humans are unique cooperators: we exchange resources and help one another in a time of need. The tendencies central to understanding the mechanics of cooperation and most useful in explaining crime are retribution and reciprocity (Bowles & Gintis, 2011). In order to test these tendencies, I organise them into a Retribution and Reciprocity Model (RRM). RRM is based on the understanding that people possess different levels of negatively reciprocal, positively reciprocal, and retributive tendencies. These tendencies interact with the individual's perceptions of the environment and elicit a response that may or may not result in a crime. This dissertation is devoted to presenting, explaining, and testing this theory. First, I synthesize everything we know about retribution and reciprocity to bring both concepts into one testable model with a mechanism of action: RRM. Second, I develop the methods to study RRM using hypothetical scenarios, a decision-making game adapted from the field of behavioural economics, as well as a psychometric inventory. Third, I use these methods to examine and test RRM as a model and learn that people are retributive and reciprocal; and that these tendencies can explain criminal behaviours. Through three separate papers we gain a full understanding of what RRM is, how it can be studied, and how it can contribute to the field of criminology. Therefore, future research can easily pick it up and integrate it with other theories of crime in order to enhance our understanding of the “black box” of human decision-making.