The Model Criminal Code (MCC) was intended to be a Code for all Australian jurisdictions. It represents a high point of faith in the value and possibility of systematising, rationalising and modernising criminal law. The core of the MCC is Chapter 2, the ‘general principles of criminal responsibility’, which outlines the ‘physical’ and ‘fault’ elements of criminal offences, and defines concepts such as recklessness. This paper assesses the MCC as a criminal law reform project and explores questions of how the MCC came into being, and why it took shape in certain ways at a particular point in time. The paper tackles these questions from two different perspectives—‘external’ and ‘internal’ (looking at the MCC from the ‘outside’ and the ‘inside’). I make two main arguments. First, I argue that, driven by a ‘top down’ law reform process, the MCC came into being at a time when changes in crime and criminal justice were occurring, and that it may be understood as an attempt to achieve stability in a time of change. Second, I argue that the significance of the principles of criminal responsibility, which formed the central pivot of the MCC, lies on the conceptual level—in relation to the language through which the criminal law is thought about, organised and reformed.