The main findings demonstrate a significant association between mindfulness and emotional reactivity, with this varying upon the dimension of mindfulness and emotional reactivity explored. Moreover, three laboratory studies have been conducted in the UK and Thailand to investigate the relationship between mindfulness and emotional reactivity as elicited by affective stimuli (pictures, non-intense video and sound clips and intense video clips). Two surveys undertaken with US and Thai samples have been performed to explore the general association between trait mindfulness, cognitive emotion regulation and emotional states (anxiety and depression). The main purpose of this thesis is therefore to explore the association between mindfulness and emotional reactivity as assessed via subjective and objective scales. Thus, an objective measure of mindfulness and emotion is needed to improve the robustness of such investigation. Additionally, respondents differ in their interpretation of items within mindfulness scales due to their background and understanding of mindfulness. Consequently, the concept held as to mindfulness is diverse and related to the background of the western scale developers. Such drawbacks involve the understanding of Westerners in mindfulness being rooted in Buddhism, an eastern religion. Yet, it is necessary to improve the quality of the measurements employed in studying mindfulness and its relationship with emotion due to the traditional subjective mindfulness scales demonstrating substantial drawbacks. Mindfulness has demonstrated its benefits in being able to enrich human mental health through its negative association with negative emotion and positive with positive emotion.