Parental monitoring of settings is not always relevant for the prevention of adolescent crime because adolescents with strong personal moral rules and the ability to exercise self control are unlikely to offend even when they are unsupervised and know that their parents have little knowledge about their activities. Parental monitoring, commonly operationalised as parental supervision or parental knowledge, is often shown to have a negative relationship with crime involvement. However, research often ignores both the mechanism by which these relationships occur and the conditions under which they might (and might not) be found. This thesis uses specialist Space-Time Budget data (from the Peterborough Adolescent and Young Adult Development Study) to allow the comparison of adolescent crime rates in settings characterised by the of convergence of i) the physical presence or absence of parents and other guardians, ii) the psychological presence or absence of parents (represented by adolescent-perceived generalised parental knowledge of the circumstances of unsupervised activity) and iii) personal crime propensity (moral rules and ability to exercise self control). The conclusion derived from the results is that the physical presence of parents and other guardians in settings reduces the rate of adolescent crime committed in those settings; and the psychological presence of parents reduces the criminogenic impact of unsupervised time. Crucially however, these effects of parental monitoring are almost irrelevant for adolescents with a lower personal crime propensity, who are not likely to offend in settings irrespective of the physical or psychological absence of parents and other guardians. These findings provide support for person-environment interactions inherent in the causal model of Situational Action Theory, and provide a novel addition to evidence that could be used in future to inform policy-relevant recommendations concerning parenting behaviour and adolescent offending. Although this thesis provides new evidence about the relationship between parental monitoring and crime, the bulk of its contribution is relevant to a much wider audience. It contributes to the debate on approaches to the study of crime and crime prevention, adds clarity to key concepts and develops theoretical arguments in the field of parental monitoring and crime, develops a novel application of Situational Action Theory, extends theoretical and methodological discussions surrounding situational analysis, applies novel data and analytical methods to the study of the psychological and physical presence of guardians, generates and situates unique findings about the situational role of aspects of parental monitoring and crime, and makes some policy recommendations and suggestions about the nature and direction of future research.