Rejection sensitivity, a propensity to perceive and act strongly to potential rejection, can impact many aspects of one’s life, including having a negative effect on mental health. With a possible detrimental effect of rejection sensitivity on stress-related disorders, it is important to gain more understanding of the subject in order to prevent and treats the negative effect of rejection sensitivity. Chapter 1, presents a literature review on the impacts of rejection sensitivity, including impacts on behaviour, cognition, physiology, and emotion. From this, a model is proposed that incorporates rejection sensitivity into Ehlers and Clark’s cognitive model of posttraumatic stress disorder (PTSD). The empirical studies of the PhD investigate different aspects of this extended theoretical framework. Chapter 2 presents findings of a cross-sectional survey in trauma survivors showing that rejection sensitivity is associated with vulnerable attachment, social support, and posttraumatic-stress disorder. The results of this study supported important aspects of the proposed theoretical model of the thesis. Chapter 3 focused on possible mechanisms how social rejection can impact the level of stress and physiological stress responses, and how individual differences in rejection sensitivity moderates these effects. The finding indicated that whilst being rejected or accepted through an experimental vignette task did not influence subjective stress level, high levels of rejection sensitivity made a significant contribution to increases in stress level following social evaluation and thus partially supported the extended theoretical model. Building on Chapter 3, Chapter 4 investigated the contribution of rejection sensitivity to the psychophysiological responses during a virtual reality lab trauma, as well as the role of subsequent rejecting or accepting social interaction on trauma recovery. No associations between rejection sensitivity and variations in physiological responses were found. Social rejection following traumatic experience also did neither contribute to increase in stress reactivity nor subsequent intrusions. This finding suggested that recovery from trauma may not be influenced by immediate social interaction following the traumatic experience and hence did not support the theoretical model. In Chapter 5, a secondary data analysis revealed that rejection sensitivity was associated with childhood trauma, substance use experiences, perceived social support, stress and depression. These findings provide support for parts of the theoretical model and highlight the importance of rejection sensitivity for trauma recovery and stress-related disorder. Chapter 6 presents an overall discussion of the findings of the thesis, including the discussion related to literature reviews; specifically, the impacts of rejection sensitivity on physiology and stress-related mental health. The chapter also provides limitations and strengths of the studies with the main focused on the methodology used for the rejection tasks. Finally, how the findings can be used as a guide for future directions, and clinical implications, were presented.