Guardianship is a core principle of situational crime prevention (Clarke, 1997). Through their presence and supervision, guardians discourage offending by increasing an offender’s risk of detection and/or apprehension and manipulating the perceived costs and rewards associated with the criminal opportunity. It is in this way that guardianship may be a mechanism for reducing the incidence or severity of sexual offences against women – particularly now that it is understood sexual offenders, much like any other individual, are capable of engaging in cost-benefit analysis as part of their decision making (Beauregard & Leclerc, 2007). Existing research exploring sexual offences against women through the lens of the criminal event points to a potential association between the presence of other persons, besides the offender and victim, and sexual offence avoidance. Less is known about who these guardians are, what they do during the crime event, and the real-life conditions under which guardianship is more or less effective against sexual offences. To build on these gaps, this thesis examined the role of guardianship in the prevention of sexual offending against women. Specifically, and by means of three individual studies, it identified to what extent and under what circumstances the presence of guardianship affects the likelihood of disruption in sexual offences against women. Study 1 evaluated all the literature on guardianship in incidents of sexual offending to establish what is currently known about how guardians can be effective in controlling sexual offences against women. This established that while guardians do play a role in prevention, the likelihood and type of intervention by available guardians varies across situational contexts. Study 2 focused on the tradition of offender-based research, and presented a self-report questionnaire incorporating a crime script framework. This allowed for a first-time comparison of completed versus disrupted sexual offences at each stage of the crime commission process and results indicated that guardianship intensity is one of two dominant mechanisms operating in the disruption of sexual offence opportunities. With a view to beginning the construction of the evidence base for prevention, Study 3 turned attention to empirical insight and the extent to which guardianship affects the likelihood of the disruption of sexual offences against adult females. Using self-reported crime event data collected from adult men convicted and incarcerated for a sexual offence against female, analyses showed that the guardianship intervention is a fundamentally important factor in sexual offence disruption. Offender decision making in the context of sexual offences against women is, however, a highly dynamic process impacted by the micro-situational context of the crime event. Implications for theory and practice are discussed.