Background: Paper I: Intensive Cognitive Behavioural Therapy (CBT) is an emerging intervention for psychological distress and mental health. There is no known review in this area in an adult population. Paper II: The InSPire programme was developed to deliver intensive cognitive behavioural suicide prevention (CBSP) therapy within a prison, to address barriers to long term engagement in previous psychological intervention studies (i.e. attrition). Aims Paper I systematically reviewed studies which have delivered intensive CBT within an adult population experiencing psychological distress. Paper II aimed to determine the feasibility of intensive CBSP in a prison, with individuals experiencing suicidal thoughts and behaviours. Methods: Paper I was a systematic review of 17 studies delivering intensive CBT across populations experiencing psychological distress associated with mental health, addiction, chronic pain and following a traumatic incident. Paper II was a feasibility case series with single baseline and single follow up. Thirteen individuals consented to the InSPire programme, delivering an intensive CBSP intervention within a three week period (five two-hourly sessions were offered). Outcome measures assessed suicidality (including thoughts of self-harm) and client satisfaction. Psychological mechanisms associated with suicide were measured, including perceived social support, emotional regulation and problem solving. Results: Paper I found promising results in the efficacy and feasibility of intensive CBT, particularly in the population experiencing distress associated with mental health difficulties. The review unearthed a number of recommendations for further research in this field. Paper II found the InSPire programme to be feasible, as determined by successful recruitment and retention across the study, including high participant satisfaction. The programme appeared to have an efficacious benefit for those who took part across all outcomes measured. Conclusions: Paper I highlights the promising feasibility and efficacy of intensive CBT, yet more rigorously designed studies (i.e. RCTs) must be conducted before firm conclusions can be drawn and prior to a future repeat review. Paper II highlighted the potential benefit of conducting intensive CBSP in prison. Given the limited generalisability of this study, a larger scale feasibility trial would now be warranted to determine more conclusive evidence. Paper III was a critical review paper appraising papers I and II. This included consideration of the methodological process, strengths and limitations, and considerations alongside further literature.