Recent research has shown that morningness is negatively correlated with the personality variable impulsivity. Additionally, a relationship between conscientiousness and morningness has been reported. As several researchers have demonstrated links between clock gene polymorphisms and diurnal preference, this thesis aims to test the possibility that there is a direct link between these polymorphisms and personality. A total of 617 participants completed an online survey consisting of well known self report questionnaires relating to personality and diurnal preference. Conscientiousness was found to be the largest predictor of diurnal preference, with associations also evident with openness to experience and agreeableness. The relationship between impulsivity and eveningness was also confirmed. 174 participants were invited to donate buccal swabs and high and low conscientiousness groups were formed from the 20% extremes of conscientiousness score. A central 20% formed an intermediate group Genotyping of these subjects in relation to clock gene polymorphisms known to associate with diurnal preference was then undertaken. No differences in genotype were observed between conscientiousness groups in any of the polymorphisms. Further analysis of possible relationships between genotype and personality variables revealed associations between CLOCK rs 11932595 and neuroticism, impulsivity and openness, before Bonferroni correction. 97 participants within the conscientiousness groups completed the GoStop behavioural test. No differences were observed between conscientiousness groups on the primary measure of the task. Furthermore, no relationship was observed between self-report and behavioural impulsivity. In relation to genotype, a longer mean stop latency was associated with PER3 VNTR 5/5 genotype, before Bonferroni correction. In conclusion, conscientiousness is the primary personality dimension associated with diurnal preference and should be considered in future studies. Moreover, two possible candidate clock gene polymorphisms that may relate to personality were also identified, the replication of which in future studies may contribute to the understanding of the underlying genetic basis of personality.