Volume 1 of the thesis contains the research component. Paper one is a systematic review of longitudinal studies looking at the association between depression and diabetes complications. Paper two describes a prospective longitudinal study, examining risk factors for postnatal depression in women with gestational diabetes. Paper three is a public dissemination document. Volume 2 of the thesis contains clinical practice reports (CPRs). The reports reflect work conducted during clinical placements, as follows: 1) psychological models CPR (A cognitive-behavioural and psychodynamic formulation in the case of Samuel, a 28-year old man with phobia of falling following an acquired brain injury); 2) service-related CPR (Adherence to initial goal planning meeting clinical standard in an outpatient brain injury rehabilitation service. Factors acting as barriers and facilitators); 3) single-case experimental design CPR (Cognitive behavioural intervention in the case of Alice, a 15-year old White British female with obsessive-compulsive symptoms); 4) case study CPR (The case of Monique, a 55-year old White British female with mild learning disabilities presenting with challenging behaviour); 5) case-study CPR – abstract (The case of Martin, a 67-year old White British male presenting with hypochondriasis). Names and other identifying materials in all the reports were changed in order to protect confidentiality.