In renal transplantation, immunosuppressants are prescribed to patients to prevent graft loss. Although the extent of adherence required for such treatment to prevent graft loss has not been determined, it is thought to be high. Despite this, research suggests adherence rates for renal transplant recipients to be only between 50% and 95%. Considering the impact of graft loss on the renal patient, the national healthcare budget and on the limited resource of donor organs, it is important to identify and understand factors that contribute to nonadherence, and thereafter to address those that are most influential. This thesis seeks to understand adherence of renal transplant recipients, and to identify the cognitive and behavioural factors influencing this behaviour. To achieve this, three main activities were performed, a literature review, an interview study and a questionnaire study, the methods and findings of which are presented following an overview of two social cognition models, used in two of the activities, and renal disease. The first activity, a comprehensive literature review, identified 55 research articles that explored factors influencing adherence of renal transplant recipients to immunosuppressant drug therapy. It included original research studies published between 1980 and 2009, and was updated in 2011. The findings were categorised into the five dimensional framework suggested by the World Health Organisation: patient- related factors; socio-economic factors; condition-related factors; therapy-related factors; and healthcare team and system-related factors. Secondly, a semi-structured interview study with 27 renal transplant recipients was conducted. The study explored their attitude towards and behaviours related to taking immunosuppressants. The interview schedule was informed by the health belief model, and framework analysis of the data identified five key themes. These were: satisfaction with renal replacement therapy; the importance of taking immunosuppressants; perception of side effects and risks; responding to side effects and risks; and 'compliance is routine'. Finally, a questionnaire was developed using the theory of planned behaviour and the findings of the previous two activities. Its purpose was to determine the predictors of renal transplant recipients' self-reported adherence and to explain their adherence. A logistic regression model of 528 survey responses suggested respondents were more likely to be highly adherent if they, in descending order of influence: had well- established habits; were unemployed; had a better prospective memory; were a shorter time post-transplantation; had higher levels of anticipated affect; and lower levels of perceived behavioural control. The thesis concludes with discussing the findings of the studies, their strengths and limitations, and their implications for practice and future research. The findings of this thesis suggest unintentional nonadherence to prevail and encourage the development of interventions which promote habit formation and maintenance.!