In an effort to reduce repeat sexual offending, some Australian jurisdictions have introduced legislation providing for the restriction of a sex offender's liberty in anticipation of future predicted crimes. The operation of preventive detention legislation relies centrally upon forensic clinician assessments of risk for future sexual offending. This legislation has raised important research questions related to the validity of the laws' assumptions on sexual recidivism and risk prediction, the characteristics of sex offenders submitted to post-sentence orders, and clinicians' standard of practice of risk assessment in this legal context. This thesis conducted a series of theoretical and empirical investigations linked to these research areas. The first study consisted of a psycho-legal analysis whereby the assumptions underpinning the laws' provisions were evaluated in light of the empirical evidence on risk prediction, sex offender recidivism, and sex offender rehabilitation. Together, the findings revealed that many of the laws' assumptions are invalid; this has implications for the efficacy of the legislation to protect the community from sexual offending. The second study empirically examined the demographic, developmental, clinical, and criminal characteristics of a sample of 50 sex offenders under post-sentence orders in Western Australia, New South Wales, and Victoria. Data was obtained from court-ordered clinical risk assessment reports. The findings described a group of demonstrably dangerous men who exhibited an early onset of sexual offending and complex psychiatric presentations, with a high prevalence of sexual deviance and antisociality. Their developmental histories were characterised by early exposure to multiple vulnerability factors such as abuse, illicit substance use, and social dislocation. Their complex and varied needs require a comprehensive treatment approach. The early onset of their offending suggests that well resourced early intervention services, such as those offered by mental health professionals, can play a critically important role in any effort to alter offending trajectories such as those exhibited in this sample. The third study empirically evaluated the standard of risk assessment practice amongst experts retained in preventive detention proceedings. Eighty-six court-ordered forensic evaluation reports prepared by 23 mental health professionals were obtained and analysed. Overall, the findings were mixed. Positively, valid structured risk assessment tools were commonly utilised. Also, there was good agreement between experts on the final risk assessment outcome, suggesting a consensus in relevant areas relating to risk assessment. However, a number of concerning results were also found (e.g., some evaluators adopted invalid risk assessment methodologies; others incorrectly applied and interpreted otherwise valid risk tools). Taken together, the findings suggest that the standard of practice of risk assessment must be raised. Recommendations for best practice were proposed.