Conscientiousness exerts a protective effect on health and longevity. Recent evidence suggests that Conscientiousness may influence future health status via the experience of stress; either directly through reduction of stress exposure, and/or indirectly by buffering the negative effects of stress. Four empirical studies were conducted using multi-method approaches to explore the relationships between Conscientiousness, daily stress, and health outcomes. Daily diaries and multi-level modelling were employed to test the effects of daily stress on physical symptoms and daily mood, and whether Conscientiousness moderated these effects. Conscientiousness, and its facets, showed direct and indirect effects: Self Control was associated with experiencing fewer, less intense daily hassles; Industriousness positively predicted positive affect; Conscientiousness also moderated the relationship between appraisals and positive affect, such that stressful appraisals predicted lower positive affect for the low conscientious group on1y. These findings demonstrate multiple ways m which Conscientiousness may affect the daily experience of stress, and the relationships between stress and daily health outcomes. Relationships between Conscientiousness, daily experience and cortisol were also explored. Day-to-day changes in daily experience and cortisol were investigated, together with the influence of Conscientiousness. Conscientiousness did not have a main effect on the cortisol awakening response (CAR) or diurnal cortisol levels. However, appraisals negatively predicted the next-day CAR, and thinking about the day's schedule in the morning positively predicted the CAR. The latter effect was moderated by Conscientiousness, such that it was significant only in the low Responsibility group. A lower CAR also predicted the experience of more physical symptoms throughout the day. Therefore, daily experiences influenced cortisol levels, but cortisol also influenced daily health outcomes, and Conscientiousness moderated some of these effects. This thesis supports the suggestion that daily stress is important in explaining, in part, the relationship between Conscientiousness and health outcomes, and highlights multiple pathways between these variables.