Sleep difficulties are prevalent among adolescents and emerging adults and are implicated in the onset and maintenance of mental health difficulties. Sleep support often involves sleep hygiene, however, this often involves supplying individuals with information on recommended behaviours and the consequences of these. Such approaches may overlook the role of longstanding routines and habitual pre-sleep behaviours, which can maintain unhelpful sleep behaviours despite knowledge. This thesis aimed to investigate how behavioural science has been applied within current approaches to changing sleep hygiene behaviours and to explore the acceptability of a habit-focused sleep hygiene intervention. Part A of this portfolio presents a scoping review and 'behavioural science audit’ of sleep hygiene interventions for adolescents and emerging adults. This review found that use of behaviour change theory in sleep hygiene interventions is rare, with a narrow focus on educational approaches and information giving techniques. This suggests that intervention-developers assume that this population lack the knowledge and conscious motivation to perform sleep hygiene recommendations. Overall few trends are seen when comparing improvements across interventions by behaviour science components, although incorporating environmental restructuring and monitoring techniques appeared promising. Findings highlighted a need for future intervention studies to report the theoretical basis of interventions and intended mechanisms of change. Part B presents an empirical paper investigating the acceptability of two variants of script elicitation, an intervention based on habit-theory, amongst undergraduate students using qualitative and quantitative methods. One abbreviated variant involved raising awareness of habitual behaviours in pre-sleep routines, and the other unabbreviated variant further involved updating cues and behaviours within routines to improve sleep hygiene. The findings suggested that both variants were acceptable to participants, though including the modification component appeared to provide added benefits beyond the abbreviated variant.