Habit change is often seen as key to successful long-term behaviour change. Making ‘good’ behaviours habitual – i.e., ensuring a behaviour is prompted automatically on exposure to situational cues, based on cue-response associations learned through context-consistent repetition – is portrayed as a mechanism for sustaining such behaviours over time. Conversely, disrupting ‘bad’ habits is expected to terminate longstanding unwanted actions. Yet, some commentators have suggested that the role of habit in real-world behaviour and behaviour change has been overstated. Such critiques highlight a gap between habit theory and the reality of human behaviour ‘in the wild’. This state-of-the-field review aims to narrow this gap. Building on a core distinction between habit and habitual behaviour, our review seeks to offer interpretations of habit theory and evidence that will better manage intervention designers’ expectations regarding how modifying habit can realistically be expected to promote behaviour change. We emphasise that habit is just one potential influence on behaviour at any given moment, and highlight instances in which habit may dominate over intention, and in which intention may dominate over habit, in determining behaviour frequency. We suggest that, while it may assist behaviour maintenance, habit formation may be neither necessary nor sufficient to sustain real-world behaviour change. We draw attention to the various ways in which habit may be ‘broken’ (i.e., disrupted), and discern the implications of each habit disruption mechanism for long-term cessation of unwanted behaviours.