This thesis investigates the effects of work-related stressors on in-role performance and work engagement. First, it explores whether stressors that have long been categorized as challenging or hindering are appraised commensurately as challenging and hindering, respectively, or whether they are appraised as both challenging and hindering simultaneously. Second, it attempts to better explain the contradictory findings surrounding the relationships between stress and in-role performance and work engagement by including stress appraisals as a mechanism driving these relationships. Finally, this thesis also looks at whether one’s beliefs about the debilitating and enhancing characteristics of stress could help to explain not only how stressors are appraised, but also how appraisals eventually influence performance and engagement. On five consecutive work days, 487 Canadian and American full-time employees were asked to report on their stress mindset and to appraise a set of eight stressors destined to capture a wide array of challenging and hindering work stressors, after which they then evaluated their performance and engagement at work. Results showed that employees rarely appraised stress as uniquely challenging or hindering and, in fact, most stressors were appraised as being both at the same time. In addition, challenge and hindrance stressors were evaluated as being less hindering and hindrance stressors were evaluated as being more challenging when employees had increasingly positive views about stress. Stress mindset was thus shown to be an important boundary condition that appears to modulate the genesis of stress appraisals. In addition, including stress appraisals was shown to be beneficial in explaining the stressors’ relationship to performance and engagement, with challenge and hindrance stressors boosting and hampering these outcomes, respectively. Although stress mindset was less effective in explaining the appraisal-to-outcome links, it nevertheless played a buffering role by reducing the negative influence of hindrance appraisals on work engagement. This research is important in clarifying some misconceptions about how workplace stressors are evaluated and in providing novel evidence that stress mindset is a key variable in the study of stress at work, in general, and that of stress appraisals, in particular.