Traumatic brain injury (TBI) increases risk of depression which is distressing and can be a barrier to recovery. This program of research examined non-pharmacological interventions for people with depression following TBI. A Cochrane systematic review was conducted in order to identify studies of interventions (Gertler, Tate, & Cameron, 2015; Chapter 2, section 1). Cochrane reviews are the most stringent form of systematic review of evidence relating to treatment outcomes. The review identified six studies, three studies relating to cognitive-behavioural therapy (CBT) which were combined in a meta-analysis that showed a very small effect in favour of treatment versus control, with a wide confidence interval. Other treatment studies were evaluated but either did not favour any treatment or were low quality studies. Recent studies have reported positive findings for CBT extended by booster sessions or for acceptance and commitment therapy (Chapter 2, section 2). Chapter 3 (Gertler & Cameron, 2018) is a published journal article explaining data analytic techniques used in a Cochrane review. Chapter 4 describes a psychometric evaluation of single-item mood scales (SIMS; Gertler & Tate, 2020) that can be used to demonstrate progress in treatment. SIMS are frequently used in clinical practice but had not yet been shown to be valid when used with people with brain impairment. SIMS were demonstrated to have construct and criterion validity when applied to TBI. Chapter 5 (Gertler and Tate, 2019) is a published journal article describing a single case experimental design (SCED) trial of behavioural activation (BA) to improve participation and mood. BA was chosen because it had not been evaluated for people with TBI and was thought to be more suitable than treatments such as CBT that require abstract thinking. The authors did not find evidence in favour of BA and this was discussed in the context of recent research findings that suggested that new technologies could improve the quality of measurement and interventions. In conclusion, there is more research to do in order to improve the effectiveness of interventions for depression after TBI however, using SIMS as a measure and SCED methodology, the thesis demonstrates a model for investigating untested interventions and their active components.